nightclothes vs jammies

nightclothes and jammies both are nouns.

Word	Noun	Adjective	Verb	Adverb
nightclothes	Yes	No	No	No
jammies	Yes	No	No	No

As nouns, jammies is a hyponym of nightclothes; that is, jammies is a word with a more specific, narrower meaning than nightclothes:

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

Other hyponyms of nightclothes include gown, night-robe, nightdress, nightgown, nightie, nightshirt, pajama, pj's, pyjama.

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