sweat pants vs trousers

sweat pants and trousers both are nouns.

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

As nouns, trousers is a hypernym of sweat pants; that is, trousers is a word with a broader meaning than sweat pants:

sweat pants: loose-fitting trousers with elastic cuffs; worn by athletes
trousers: (usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately

Other hypernyms of sweat pants include pair of trousers, pant.

sweat pants (noun)	trousers (noun)
loose-fitting trousers with elastic cuffs; worn by athletes	(usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately