drinker vs sipper

drinker and sipper both are nouns.

Word	Noun	Adjective	Verb	Adverb
drinker	Yes	No	No	No
sipper	Yes	No	No	No

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

Other hyponyms of drinker include gulper, guzzler, quaffer, sucker.

drinker (noun)	sipper (noun)
a person who drinks alcoholic beverages (especially to excess)	a drinker who sips
a person who drinks liquids