stretch pants vs trousers

stretch pants and trousers both are nouns.

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

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

stretch pants: trousers made of a stretchy fabric
trousers: (usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately

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

stretch pants (noun)	trousers (noun)
trousers made of a stretchy fabric	(usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately