bellbottom pants vs bellbottom trousers

bellbottom pants and bellbottom trousers both are nouns.

Word	Noun	Adjective	Verb	Adverb
bellbottom pants	Yes	No	No	No
bellbottom trousers	Yes	No	No	No

As nouns, bellbottom pants and bellbottom trousers are synonyms defined as:

bellbottom pants and bellbottom trousers: (used in the plural) trousers with legs that flare; worn by sailors; absurdly wide hems were fashionable in the 1960s

Other synonyms of bellbottom pants include bell-bottoms.

bellbottom pants (noun)	bellbottom trousers (noun)
(used in the plural) trousers with legs that flare; worn by sailors; absurdly wide hems were fashionable in the 1960s	(used in the plural) trousers with legs that flare; worn by sailors; absurdly wide hems were fashionable in the 1960s