nightdress vs intimate apparel

nightdress and intimate apparel both are nouns.

Word	Noun	Adjective	Verb	Adverb
nightdress	Yes	No	No	No
intimate apparel	Yes	No	No	No

As nouns, intimate apparel is a hypernym of nightdress; that is, intimate apparel is a word with a broader meaning than nightdress:

nightdress: lingerie consisting of a loose dress designed to be worn in bed by women
intimate apparel: women's underwear and nightclothes

Other hypernyms of nightdress include lingerie, nightclothes, nightwear, sleepwear.

nightdress (noun)	intimate apparel (noun)
lingerie consisting of a loose dress designed to be worn in bed by women	women's underwear and nightclothes