https://dic.pixiv.net/a/錬成
https://en.wiktionary.org/wiki/錬成

Not a synonym of 錬金術.

@@ -26 +25,0 @@
-<xref type="see" seq="1559970">錬金術・1</xref>
@@ -28 +27,2 @@
-<gloss>alchemy</gloss>
+<gloss>use of alchemy</gloss>
+<gloss>producing (gold, etc.) with alchemy</gloss>

Both GG5 and gloss it this way.
Daijisen: 心身・技術などを鍛えて立派なものにすること。Daijirin is similar.
Wiktionary -2nd sense.

I suspect that's the second sense, which is mentioned in Wiktionary.

@@ -18,0 +19,10 @@
+<gloss>strengthening</gloss>
+</sense>
+<sense>
+<stagk>錬成</stagk>
+<pos>&n;</pos>
+<pos>&vs;</pos>
+<pos>&vt;</pos>
+<xref type="see" seq="1559970">錬金術・1</xref>
+<s_inf>in modern fiction</s_inf>
+<gloss>alchemy</gloss>

https://i.imgur.com/QwAm5eC.png
https://ja.wikipedia.org/wiki/錬金術

I think the definition for this entry is a bit lacking - as shown in the first link above, that's an item description from a videogame made by a japanese developer, and judging by the usage of 練成 there I would assume the meaning is something on the lines of "a lump of metal refined from copper ore".
In the second link about 錬金術　錬成 (the one using 錬 ) appears in this sentence: "金属に限らず様々な物質や人間の肉体や魂をも対象として、それらをより完全な存在に錬成する試みを指す。"  and in this sentence as well I don't think the meanings of "training/drilling" would fit, so I would suggest the addition of something like "refining", maybe?

Meikyo vt and vi additions to n,vs entries
-*- via bulkupd.py -*-

@@ -15,0 +16 @@
+<pos>&vt;</pos>