pj's vs sleepwear

pj's and sleepwear both are nouns.

Word	Noun	Adjective	Verb	Adverb
pj's	Yes	No	No	No
sleepwear	Yes	No	No	No

As nouns, sleepwear is a hypernym of pj's; that is, sleepwear is a word with a broader meaning than pj's:

pj's: (usually plural) loose-fitting nightclothes worn for sleeping or lounging; have a jacket top and trousers
sleepwear: garments designed to be worn in bed

Other hypernyms of pj's include nightclothes, nightwear.

pj's (noun)	sleepwear (noun)
(usually plural) loose-fitting nightclothes worn for sleeping or lounging; have a jacket top and trousers	garments designed to be worn in bed