achene vs key fruit

achene and key fruit both are nouns.

Word	Noun	Adjective	Verb	Adverb
achene	Yes	No	No	No
key fruit	Yes	No	No	No

As nouns, key fruit is a hyponym of achene; that is, key fruit is a word with a more specific, narrower meaning than achene:

achene: small dry indehiscent fruit with the seed distinct from the fruit wall
key fruit: a winged often one-seed indehiscent fruit as of the ash or elm or maple

Other hyponyms of achene include key, samara.

achene (noun)	key fruit (noun)
small dry indehiscent fruit with the seed distinct from the fruit wall	a winged often one-seed indehiscent fruit as of the ash or elm or maple