sweet pepper vs pepper

sweet pepper and pepper both are nouns.

Word	Noun	Adjective	Verb	Adverb
sweet pepper	Yes	No	No	No
pepper	Yes	No	Yes	No

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

sweet pepper: large mild crisp thick-walled capsicum peppers usually bell-shaped or somewhat oblong; commonly used in salads
pepper: sweet and hot varieties of fruits of plants of the genus Capsicum

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

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

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

sweet pepper (noun)	pepper (noun)
large mild crisp thick-walled capsicum peppers usually bell-shaped or somewhat oblong; commonly used in salads	pungent seasoning from the berry of the common pepper plant of East India; use whole or ground
plant bearing large mild thick-walled usually bell-shaped fruits; the principal salad peppers	sweet and hot varieties of fruits of plants of the genus Capsicum
	any of various tropical plants of the genus Capsicum bearing peppers
	climber having dark red berries (peppercorns) when fully ripe; southern India and Sri Lanka; naturalized in northern Burma and Assam

sweet pepper (verb)	pepper (verb)
	attack and bombard with or as if with missiles
	add pepper to