Rare term referring to established or conventional usage, particularly in language. Often replaced by 語法 or 使い方 in modern Japanese.
See also: 語法
This expression has become established as conventional usage.
使い方 is a general, everyday word for 'how to use' something, not limited to language, and is much more common than 慣用法.
Compound of 慣用 (customary use) and 法 (method, rule). The exact historical derivation is uncertain, but the term follows standard Sino-Japanese word formation patterns.