slacks vs trousers

slacks and trousers both are nouns.

Word	Noun	Adjective	Verb	Adverb
slacks	Yes	No	No	No
trousers	Yes	No	No	No

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

slacks: (used in the plural) pants for casual wear
trousers: (usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately

Other hypernyms of slacks include pair of trousers, pant.

slacks (noun)	trousers (noun)
(used in the plural) pants for casual wear	(usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately