Consider the idiomatic phrase 'having said that', or certain words that have become prepositions, such as 'concerning', 'regarding', 'respecting', 'following' and so on.

Although proverb and saying are practically synonymous, the same can not be said about idiomatic phrase and four-character idiom.

Yet these are idiomatic phrases that even obdurate sticklers would have a hard time objecting to.

Idiomatic phrases are often used to stereotype people.

They express themselves in brief idiomatic phrases, and the language has neither singular nor plural.