Where does the れ reading of 落 in 洒落 come from?

Question

Both wiktionary and jisho.org list the on'yomi for 落ちる as ラク. The kun'yomi is 落{お}ちる, 落{お}とす, or 落{お}ち. So I'm wondering how this kanji developed the reading れ in お洒落{しゃれ} and 洒落{しゃれ}.

Answer 1

Technically れ is not a reading of 落, しゃれ is a reading of 洒落. A reading which ignores the usual reading of the characters.

I think it is arguable whether this is:

当て字:assigning kanji to words for their phonetic value, ignoring their semantic value. This is often used for e.g. native Japanese geographical names, like 恵比寿, えびす.

熟字訓:assigning multiple kanji to (usually native Japanese) words based on their semantics, but ignoring the morphemes they usually represent. A commonly used example would be the あす reading of 明日.

If we believe the etymology on http://gogen-allguide.com/si/syare.html, 洒落 originally had a reading of しゃらく, which meant something like "frank, carefree", but started to be used for しゃれ for both its phonetic similarity and semantic similarity.

So maybe the most precise decription is to say that it's both an imperfect 当て字 and an imperfect 熟字訓.