Yojijukugo

For example, the compound word okunaikin'en (屋内禁煙, "no smoking indoors") is a non-idiomatic yojijukugo.

It is made up of four characters: oku (屋, building), nai (内, inside), kin (禁, prohibited), and en (煙, smoking).

Alternatively, it can be regarded as consisting of two common two-character compounds: okunai (屋内, indoors), and kin'en (禁煙, prohibition of smoking).

An example of the highly idiomatic compound is: "Ocean-thousand, mountain-thousand" means "a sly old fox" or someone who has had all sorts of experience in life so that they can handle, or wiggle out of, any difficult situations through cunning alone.

The entries in the published dictionaries of yojijukugo are typically limited to these idiomatic compounds of various origins.