pimiento vs capsicum

pimiento and capsicum both are nouns.

Word	Noun	Adjective	Verb	Adverb
pimiento	Yes	No	No	No
capsicum	Yes	No	No	No

As nouns, capsicum is a hypernym of pimiento; that is, capsicum is a word with a broader meaning than pimiento:

pimiento: plant bearing large mild thick-walled usually bell-shaped fruits; the principal salad peppers
capsicum: any of various tropical plants of the genus Capsicum bearing peppers

Other hypernyms of pimiento include capsicum pepper plant, pepper.

pimiento (noun)	capsicum (noun)
fully ripened sweet red pepper; usually cooked	any of various tropical plants of the genus Capsicum bearing peppers
plant bearing large mild thick-walled usually bell-shaped fruits; the principal salad peppers