Yikes, no sombrero, I did *not* mean to revert your edit, which means there must still be some race conditions lying around here with overlapping edits.

I must have been writing a reply to Jim... then hit "next", then I saw your comments, went back, added some comments about your notes on rarity... I didn't see your edits because as soon as I hit "next", my version (Jim's version), clobbered yours... So I read your notes, and didn't realize you'd made changes.

And then I posted and reverted all of your changes.  I'll have to be careful about this...  My apologies to everyone.

So my [2] was the previous [2].  I only meant to say that the grammatical usage was far more common than all of these [rare] noun senses, and this term is not itself [rare]. Right now it looks like it is.

So, yes, to be clear, my belief is that the grammatical senses of 反面 should be all be copy/pasted straight into this entry with xrefs (maybe just one way, from here to there).  They should probably be the leading senses.  And who knows, we might even decide there is a subtle nuance meriting slight deviation in the glosses.  If not today, maybe tomorrow.

It's not elegant, but we do it all the time, and with xrefs it is not hard to maintain.  I think it yields the most practical result for end-users.

And it's nice to see a new (to me) face here on a few edits.  I meant my comments as discussion, not so much as feedback :)

GG5 (3 senses):
1 〔顔の半分〕 half the face; a half face; (横顔) a profile.
2 〔ある面の半分〕 half the surface 《of…》.
3 〔物事の一面〕 one side; (a) half; 〔他面〕 the other side; the reverse; the contrary; the opposite.
Daijisen and Daijirin have much the same.

I'd be comfortable with lining it up with GG5. etc. approach.

@@ -20,0 +21,6 @@
+<gloss>profile</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
+<pos>&adj-no;</pos>
+<misc>&rare;</misc>
@@ -22 +28 @@
-<gloss>half</gloss>
+<gloss>a half</gloss>
@@ -23,0 +30,9 @@
+<gloss>the reverse</gloss>
+<gloss>the contrary</gloss>
+<gloss>the opposite</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
+<pos>&adj-no;</pos>
+<misc>&rare;</misc>
+<gloss>half the surface (of)</gloss>

Firstly, your reasoning on [rare] makes sense (to me at least) after thinking a bit about it. 
Though, as you've noted as well, it shouldn't stay a single-sense entry like this.

That's why I'm a bit confused as to what this entry should be now. Did you mean to fully revert my proposed edit? 
I didn't quite get that feeling from your reply.
I'm sure we can incorporate the [rare] aspect into that version as well somehow.

I also need some clarification on "And sense [2] is 1000 times more common than [1]. (maybe not exactly that, but it's a big gap)."
Are you referring to sense 2 in your original proposed edit, or sense 2 in my edit proposed after that?

＞For my part, I find these note-based approaches kind of weird, and think that they are frequently overlooked by users (myself included). 
I'd argue that's really a problem of representation on the dictionary side itself though. But I get where you are coming from.

＞The primary use of 半面 is in the grammatical structure, not the single sense that has been left here.
I totally agree; that's why I attempted expanding it to a multiple-sense entry here.


Lastly, I appreciate the feedback.

For my part, I find these note-based approaches kind of weird, and think that they are frequently overlooked by users (myself included). 

The primary use of 半面 is in the grammatical structure, not the single sense that has been left here.  Yet when people search 半面, this will be the first thing they see, and it won't be helpful.  Further, while it is 10% of the usage of 反面, it's still 175,000 ngrams. It's not a rare term, but this setup makes it seem like it is.

Sombrero1, I waffled on [rare] on [1] here, and if it's dropped, I won't lose sleep on it.  But when [rare] seems a bit borderline, I think about "the greater good".  My conclusion from talking to others and chatting with chatgpt is that any non-native ad-hoc attempt to use 半面, based on the English glosses, will probably be a mistake.  We have "super common English gloss" ("the other side") paired with "super-uncommon Japanese term".  Likelihood of misunderstanding is high (Especially orally, with the overlap with 反面).  Even if not strictly "rare", I think [1] is at *least* "not common". 

I lean toward [rare] here because I think "DO NOT ATTEMPT TO USE THIS" is sound advice.  At the same time 半面 is so literal that it would easily be understood in the contexts one might find it.  Learners will still learn the term because sense[2] is not rare at all.  So, very little downside.

I used to argue that 2000 ngrams was never [rare].  I've since reformed.  Comparative rarity has some relevance.  All of the glosses here would be better expressed by terms 1000 times more common in Japanese.  And sense [2] is 1000 times more common than [1]. (maybe not exactly that, but it's a big gap).

That's why I went with [rare], anyway.

I did read the split into 3 senses on 反面, I think it's excellent.

@@ -17,25 +16,0 @@
-<pos>&conj;</pos>
-<pos>&prt;</pos>
-<xref type="see" seq="1481000">反面・1</xref>
-<xref type="see" seq="1481000">反面・1</xref>
-<s_inf>after the attributive form of a verb or adjective, or the particle の</s_inf>
-<gloss>while</gloss>
-<gloss>although</gloss>
-<gloss>though</gloss>
-<gloss>but</gloss>
-</sense>
-<sense>
-<pos>&conj;</pos>
-<xref type="see" seq="1481000">反面・2</xref>
-<xref type="see" seq="1481000">反面・2</xref>
-<xref type="see" seq="1006940">その半面</xref>
-<gloss>(but) at the same time</gloss>
-<gloss>on the other hand</gloss>
-<gloss>then again</gloss>
-<gloss>and yet</gloss>
-</sense>
-<sense>
-<pos>&n;</pos>
-<gloss>half (of a surface or area)</gloss>
-</sense>
-<sense>
@@ -43,0 +19,2 @@
+<misc>&rare;</misc>
+<gloss>half the face</gloss>
@@ -45,11 +22,2 @@
-<gloss>one half</gloss>
-<gloss>other side</gloss>
-<gloss>(the) contrary</gloss>
-<gloss>(the) opposite (side)</gloss>
-</sense>
-<sense>
-<pos>&n;</pos>
-<misc>&form;</misc>
-<gloss>half the face</gloss>
-<gloss>(a) half face</gloss>
-<gloss>profile</gloss>
+<gloss>half</gloss>
+<gloss>the other side</gloss>

（１）Sankoku
一｟名｠
  ①かたほうの面。一面。
  「建物の━に日が当たる・気むずかし屋の━がある・━の真理〔＝一方だけから見た、絶対的でない真理〕」
  ②⇨反面（一）②。 ➡ Sense 1 in the current 反面 entry
  ③〔文〕顔の半分。
  「━を布でおおう」
  ④一つの面の半分。
  「新聞の━を使った広告」
二｟接｠
  ⇨反面（二）。 ➡Sense 2 in the current 反面 entry

（２）
Virtually every kokugo keeps 顔の半分 separate.
On top of that, most kokugos split the following we currently have into 3 distinct senses
"[1][n,adj-no][rare]
  half the face; one side; half; the other side"

（３）
As for JEs, compare:
GG5: 	1 〔顔の半分〕 half the face; a half face; (横顔) a profile.
	2 〔ある面の半分〕 half the surface 《of…》.
		●(テニス)コートの半面 half the court; one side (of the net).
	3 〔物事の一面〕 one side; (a) half; 〔他面〕 the other side; the reverse; the contrary; the opposite.

Prog:   1〔表面の半分〕
	ここからは彼の顔の半面しか見えない
	   I can see only 「his profile [one side of his face] from here.
	（テニスコートの）半面を使わせていただけますか
	   May we use half the (tennis) court?
	2〔一面〕
	彼の言ったことには半面の真理がある
	   What he said was a half truth.
	その説には半面の真理しかない
	   The theory is only partially true.
	3〔一方〕 ⇒はんめん（反面）
	この本は結構面白いが，半面たわいない
	   This book is amusing [entertaining] enough, but in some respects it is childish.

（４）BCCWJ (Counts in brackets are for 反面):
半面 has 250 counts in total (1069)

Sense one:
｛〘活用形＝連体形〙｝｛半面｝＝ 58 (456)
｛〘活用形＝連体形〙｝｛半面｝｛、｝＝ 45 (314)

Sense two:
｛、｝｛半面｝＝ 21 (117)
｛、｝｛半面｝｛、｝＝ 7 (68)
｛。｝｛半面｝＝  72 (100)
｛。｝｛半面｝｛、｝＝ 63 (62)
｛〘品詞＝連体詞〙｝｛半面｝＝ 42 (212)
Note that there may be a few missing for the counts with commas, as some of the sentences used , instead of 、.

That's 157 (45 + 7 + 63 + 42) out of 250 hits for conjunctive usage (I didn't use the counts for｛。｝｛半面｝and｛、｝｛半面｝on purpose, as they could technically include false hits for noun usage). That makes 62.8% of total usage.
Based on that I put the conjunctive senses first, as in the 反面 entry.

Points （５）～（９）, as the submission would otherwise exceed the maximum URL length
https://pastebin.com/VYXPvAVn

.

I don't think this is sufficient.
[rare] should probably be dropped here, arguably from 反面 as well.

I'm proposing this expanded and aligned version, subject to further improvement.

Brian:
＞I've got a Waseda University grammar book in my hand, and the section is ~反面・~半面 (i.e. same usage).
＞Sense [1] on the two terms is distinct, and I don't think the entries should be merged.

Based on what Brian said, and what I have provided in （１）～（４）, I would argue that 反面 and 半面 should be kept in separate entries.
However, I too believe they can be aligned for the conjunctive senses together with xrefs to 反面 from this entry.
They should indeed not be merged.

Since brian has brought it up already, do we want to overtly have something along the lines of a 使い分け for sense 2 (and maybe 1 as well)?
See e.g.（６）.
Based on（９）sense 4, and examples I've seen similar to the one there, I'm wondering whether [adv] should still be included as a secondary PoS for all the conjunctive senses in both entries. Opinions?

@@ -16,0 +17,25 @@
+<pos>&conj;</pos>
+<pos>&prt;</pos>
+<xref type="see" seq="1481000">反面・1</xref>
+<xref type="see" seq="1481000">反面・1</xref>
+<s_inf>after the attributive form of a verb or adjective, or the particle の</s_inf>
+<gloss>while</gloss>
+<gloss>although</gloss>
+<gloss>though</gloss>
+<gloss>but</gloss>
+</sense>
+<sense>
+<pos>&conj;</pos>
+<xref type="see" seq="1481000">反面・2</xref>
+<xref type="see" seq="1481000">反面・2</xref>
+<xref type="see" seq="1006940">その半面</xref>
+<gloss>(but) at the same time</gloss>
+<gloss>on the other hand</gloss>
+<gloss>then again</gloss>
+<gloss>and yet</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
+<gloss>half (of a surface or area)</gloss>
+</sense>
+<sense>
@@ -19 +44,9 @@
-<misc>&rare;</misc>
+<gloss>one side</gloss>
+<gloss>one half</gloss>
+<gloss>other side</gloss>
+<gloss>(the) contrary</gloss>
+<gloss>(the) opposite (side)</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
+<misc>&form;</misc>
@@ -21,3 +54,2 @@
-<gloss>one side</gloss>
-<gloss>half</gloss>
-<gloss>the other side</gloss>
+<gloss>(a) half face</gloss>
+<gloss>profile</gloss>

Reopen.

I meant dropping the whole sense from here. I'll set up both, approve, and reopen.

@@ -24,8 +23,0 @@
-</sense>
-<sense>
-<pos>&conj;</pos>
-<xref type="see" seq="1481000">反面・2</xref>
-<xref type="see" seq="1481000">反面・2</xref>
-<misc>&form;</misc>
-<gloss>(but) on the other hand</gloss>
-<gloss>(but) at the same time</gloss>

Compare:
半面が	1683	0.9%
半面は	1773	1.0%
半面を	4124	2.3%
半面	175570	95.9%

反面	1614810	99.8%
反面が	878	0.1%
反面は	980	0.1%
反面を	952	0.1%

https://kotobank.jp/word/半面-607367
１ 顔の半分。
２ ある広さの表面の半分。「テニスコートの半面を使う」
３ 物事の片方の面。一面。「問題の半面しか見ない」「父親としてのやさしい半面もある」

https://kotobank.jp/word/反面-607366#w-607366
１ 反対の面。反対の方面。
２ （副詞的に用いて）他の面から見る場合。他面。「水に強い反面、熱に弱い」

How do they differ? (subtle)
https://chatgpt.com/share/691fdd58-8580-8008-a4d0-8bee8779fa28

Not clear to me if you're proposing dropping/merging this. daijs has distinct entries for the two terms, and this term has a distinct, uncommon-but-useful noun sense [1] that 反面 does not.

These (as I understand it) are independent derivations, one from 半 (half), one from 反 (opposing), that coincidentally have the same pronunciation and overlapping uses.

If you take daij's example:
"テニスコートの半面" (common)　vs "テニスコートの反面" (rare), you can see the underlying literal meaning differs.  
コート半面	595	65.2%
コートの半面	293	32.1%
コート反面	25	2.7%　<-- mistakes, most likely
コートの反面	0	0.0%

I dropped "reverse" and "contrary" off of [1], if that's the [n] sense. Those seem to be derived by working backwards from English grammar translations.

Eijiro's 半面の真理 is probably "a partial truth".  There's an [adj-no] usage to 半面 that also does not exist on 反面.

I waffled on [rare] on 半面, but it seems true that it's "not productive".  Less rare than 反面, but you probably shouldn't try to use it unless you've learned it in a specific collocation.

@@ -18,0 +19 @@
+<misc>&rare;</misc>
@@ -23,2 +23,0 @@
-<gloss>the reverse</gloss>
-<gloss>the contrary</gloss>

What might be better is to have 半面 as a hidden form in the 反面 entry, and an "occ. 半面" note on sense 2 there.

その反面	231331	94.3% <- the xref form *is* way more common, and should usually be preferred in almost all contexts
その半面	13629	5.6%

Explanation of the two terms
https://nihongo-online.jp/net/index.php?key=bbjgig41h-81
まず、
反面（半面）は・・一つ（一人）の中にＡ・Ｂと相反する傾向・性質が存在する
 
・父は日頃優しい反面、怒ると怖い。

そして、反面と半面の使い分けですが、これは明確なルールがなく、使う人の感覚的なものもあるように思います。
対立していると思うなら、『反面』となりますし、そうじゃないなら『半面』とする。
しかし、強いて言うなら
 
『反面』は、対立する内容を述べるときに使い、		
『半面』は、必ずしも対立しているとは限らない		
両面持ち合わせている片一方について述べるときに使う

https://chatgpt.com/share/691ab6a0-de08-8008-af3e-d3f28e4f95c1

Practical takeaway
If you’re translating or writing:
If you mean “on the other hand / conversely” → 反面
If you mean “one aspect of something with two sides” → 半面
In many contrastive sentences, either can appear, but 反面 is more idiomatic.

No, 半面 and 反面 are not adverbial expressions.
They are nouns that behave as conjunctive phrases when attached to a preceding clause, creating contrastive relationships—functionally adverbial, but not grammatically adverbs.

I've got a Waseda University grammar book in my hand, and the section is ~反面・~半面 (i.e. same usage).

That said, I talked to a Japanese college grad/language-teacher, and she was surprised to see 半面 used this way at all. Sense [1] on the two terms is distinct, and I don't think the entries should be merged.

*That* said, it's not hard to get legitimate examples:
Title: ロボット化が進み便利になる半面、人間はいなくなる？
https://weekly-economist.mainichi.jp/articles/20250916/se1/00m/020/016000c

Content: 新興国は、工業化や資源の輸出により顕著な成長を遂げた国だが、その半面、先進国並みの高所得国になっても、...
https://weekly-economist.mainichi.jp/articles/20230418/se1/00m/020/011000c

The teacher suggested these could be replaced with 反面 and be fine (and that she would have written 反面). 

Subtle nuance difference, but I think grammatically interchangeable.  (Waseda text doesn't even attempt to explain a nuance difference, and uses 反面 for all examples). 

Shouldn't this be a conjunction (like 一方), not an adverb? (see xref, which was marked as an adverb...)

Chatgpt's elegant explanation　is consistent with nihongo-online.jp ref.  Doesn't have the required sense of opposition that 反面 has.  This makes it closer to 一方, and I took "but at the same time" from there.

@@ -25,0 +26,7 @@
+<sense>
+<pos>&conj;</pos>
+<xref type="see" seq="1481000">反面・2</xref>
+<misc>&form;</misc>
+<gloss>(but) on the other hand</gloss>
+<gloss>(but) at the same time</gloss>
+</sense>