Ah, yeah, I've heard it as 円を描く too. Sure, 
it's not just maths.

> the dictionary style is to put the most common meaning first
That's never been a hard-and-fast rule, though. We'll often put less common senses first, e.g. when there's a literal and figurative meaning.
The major JEs also tend to put more common senses first but they all lead with "circle" in this case.
---
I've heard 円/えん used for "circle" plenty of times (usually as 円を描く). Not as common as まる but it's not just a maths term.

https://jmania.net/maru-en/
丸と円の違いって何？どう使い分けるのが正しいの？
「丸」と「円」。
どちらも「まる」と読みますよね。

The most common reading of 円 when it means 
"circle" might very well be "maru", also. 
(outside of mathematics, etc)
I can't actually recall ever having heard えん 
refer to a circle in any casual conversation, 
to the best of my recollection it's always ま
る. Maybe the "circle" sense here should 
actually have a math tag? See wiki for 
instance: 
https://ja.m.wikipedia.org/wiki/円_(%E
6%95%B0%E5%AD%A6)

But... the dictionary style is to put the most 
common meaning first. Esp. when we're talking 
spoken language, "yen" must be more than 2 
orders of magnitude more common as a meaning 
for 円 than "circle" is. I don't think　we 
should make ad-hoc exceptions on the fly 
either, if "circle" should come first, then we 
should implement a concise and clear rule/test 
for when a less common meaning should 
supersede the most common one.

I don't think it matters that "yen" is more common. 円/circle is an extremely common and basic word. Looks odd having it after the currency sense.

"yen" is the more common meaning by far, so I 
disagree. （I don't think the note is needed 
either.）

Surely the circle sense should come first. No ref leads with "yen".

looks better like this to me (on account of the shortness)

@@ -22,2 +22 @@
-<gloss>yen</gloss>
-<gloss g_type="expl">Japanese monetary unit</gloss>
+<gloss>yen (Japanese monetary unit)</gloss>

They can, but this dictionary is not really open for adding 旧仮名 versions of readings. I see it sneaked into the 恵比寿 entry.
Leave that to the kokugos.

@@ -20,4 +19,0 @@
-<r_ele>
-<reb>ゑん</reb>
-<re_restr>圓</re_restr>
-</r_ele>

My apologies for using this as a test.  I'm trying to see if the pre-WWII 歴史的仮名遣 kana / pronunciations can be entered.

@@ -19,0 +20,4 @@
+<r_ele>
+<reb>ゑん</reb>
+<re_restr>圓</re_restr>
+</r_ele>

moved まる into the entry for 丸

@@ -20,3 +20,0 @@
-<r_ele>
-<reb>まる</reb>
-</r_ele>
@@ -24,1 +21,0 @@
-<stagr>えん</stagr>
@@ -26,2 +22,2 @@
-<gloss>Yen</gloss>
-<gloss>money</gloss>
+<gloss>yen</gloss>
+<gloss g_type="expl">Japanese monetary unit</gloss>
@@ -31,0 +27,1 @@
+<s_inf>orig. meaning</s_inf>

@@ -9,0 +9,4 @@
+</k_ele>
+<k_ele>
+<keb>圓</keb>
+<ke_inf>&oK;</ke_inf>