plum vs cherry plum

plum and cherry plum both are nouns.

Word	Noun	Adjective	Verb	Adverb
plum	Yes	No	No	Yes
cherry plum	Yes	No	No	No

As nouns, cherry plum is a hyponym of plum; that is, cherry plum is a word with a more specific, narrower meaning than plum:

plum: any of numerous varieties of small to medium-sized round or oval fruit having a smooth skin and a single pit
cherry plum: an edible fruit of the small tree Prunus cerasifera.

Other hyponyms of plum include damson, damson plum, greengage, greengage plum, beach plum, sloe, Victoria plum.

As nouns, cherry plum is a hyponym of plum; that is, cherry plum is a word with a more specific, narrower meaning than plum:

plum: any of several trees producing edible oval fruit having a smooth skin and a single hard stone
cherry plum: small Asiatic tree bearing edible red or yellow fruit

plum (noun)	cherry plum (noun)
a highly desirable position or assignment	an edible fruit of the small tree Prunus cerasifera.
any of numerous varieties of small to medium-sized round or oval fruit having a smooth skin and a single pit	small Asiatic tree bearing edible red or yellow fruit
any of several trees producing edible oval fruit having a smooth skin and a single hard stone

plum (adverb)	cherry plum (adverb)
exactly
completely; used as intensifiers