bell-bottoms vs trousers

bell-bottoms and trousers both are nouns.

Word	Noun	Adjective	Verb	Adverb
bell-bottoms	Yes	No	No	No
trousers	Yes	No	No	No

As nouns, trousers is a hypernym of bell-bottoms; that is, trousers is a word with a broader meaning than bell-bottoms:

bell-bottoms: (used in the plural) trousers with legs that flare; worn by sailors; absurdly wide hems were fashionable in the 1960s
trousers: (usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately

Other hypernyms of bell-bottoms include pair of trousers, pant.

bell-bottoms (noun)	trousers (noun)
(used in the plural) trousers with legs that flare; worn by sailors; absurdly wide hems were fashionable in the 1960s	(usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately