ski pants vs trousers

ski pants and trousers both are nouns.

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

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

ski pants: trousers usually of stretch material and kept taut by a strap under the foot, worn for skiing or as a fashion garment.
trousers: (usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately

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

ski pants (noun)	trousers (noun)
trousers usually of stretch material and kept taut by a strap under the foot, worn for skiing or as a fashion garment.	(usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately