bird pepper vs capsicum

bird pepper and capsicum both are nouns.

Word	Noun	Adjective	Verb	Adverb
bird pepper	Yes	No	No	No
capsicum	Yes	No	No	No

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

bird pepper: plant bearing very small and very hot oblong red fruits; includes wild forms native to tropical America; thought to be ancestral to the sweet pepper and many hot peppers
capsicum: any of various tropical plants of the genus Capsicum bearing peppers

Other hypernyms of bird pepper include capsicum pepper plant, pepper.

bird pepper (noun)	capsicum (noun)
plant bearing very small and very hot oblong red fruits; includes wild forms native to tropical America; thought to be ancestral to the sweet pepper and many hot peppers	any of various tropical plants of the genus Capsicum bearing peppers