pantaloon vs pair of trousers

pantaloon and pair of trousers both are nouns.

Word	Noun	Adjective	Verb	Adverb
pantaloon	Yes	No	No	No
pair of trousers	Yes	No	No	No

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

pantaloon: trousers worn in former times
pair of trousers: (usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately

Other hypernyms of pantaloon include pant, trousers.

pantaloon (noun)	pair of trousers (noun)
trousers worn in former times	(usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately