bar fly vs drinker

bar fly and drinker both are nouns.

Word	Noun	Adjective	Verb	Adverb
bar fly	Yes	No	No	No
drinker	Yes	No	No	No

As nouns, drinker is a hypernym of bar fly; that is, drinker is a word with a broader meaning than bar fly:

Other hypernyms of bar fly include imbiber, juicer, toper.

bar fly (noun)	drinker (noun)
a drinker who frequents bars	a person who drinks alcoholic beverages (especially to excess)
	a person who drinks liquids