set phrase vs rusticism

set phrase and rusticism both are nouns.

Word	Noun	Adjective	Verb	Adverb
set phrase	Yes	No	No	No
rusticism	Yes	No	No	No

As nouns, rusticism is a hyponym of set phrase; that is, rusticism is a word with a more specific, narrower meaning than set phrase:

set phrase: an expression whose meanings cannot be inferred from the meanings of the words that make it up
rusticism: a rural idiom or expression

Other hyponyms of set phrase include ruralism.

set phrase (noun)	rusticism (noun)
an expression whose meanings cannot be inferred from the meanings of the words that make it up	a rural idiom or expression