drink vs nightcap

drink and nightcap both are nouns.

Word	Noun	Adjective	Verb	Adverb
drink	Yes	No	Yes	No
nightcap	Yes	No	No	No

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

drink (noun)	nightcap (noun)
the act of drinking alcoholic beverages to excess	the final game of a double header
the act of swallowing	a cloth cap worn in bed
any liquid suitable for drinking	an alcoholic drink taken at bedtime; often alcoholic
a single serving of a beverage
any large deep body of water

drink (verb)	nightcap (verb)
be fascinated or spell-bound by; pay close attention to
take in liquids
consume alcohol
drink excessive amounts of alcohol; be an alcoholic
propose a toast to