shorts vs pair of trousers

shorts and pair of trousers both are nouns.

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

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

shorts: (used in the plural) trousers that end at or above the knee
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 shorts include pant, trousers.

shorts (noun)	pair of trousers (noun)
(used in the plural) trousers that end at or above the knee	(usually in the plural) a garment extending from the waist to the knee or ankle, covering each leg separately
underpants worn by men