sweet pepper vs sweet pepper plant

sweet pepper and sweet pepper plant both are nouns.

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

As nouns, sweet pepper and sweet pepper plant are synonyms defined as:

sweet pepper and sweet pepper plant: plant bearing large mild thick-walled usually bell-shaped fruits; the principal salad peppers

Other synonyms of sweet pepper include bell pepper, Capsicum annuum grossum, paprika, pimento, pimiento.

sweet pepper (noun)	sweet pepper plant (noun)
large mild crisp thick-walled capsicum peppers usually bell-shaped or somewhat oblong; commonly used in salads	plant bearing large mild thick-walled usually bell-shaped fruits; the principal salad peppers
plant bearing large mild thick-walled usually bell-shaped fruits; the principal salad peppers