complainer vs kvetch

complainer and kvetch both are nouns.

Word	Noun	Adjective	Verb	Adverb
complainer	Yes	No	No	No
kvetch	Yes	No	Yes	No

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

complainer (noun)	kvetch (noun)
a person given to excessive complaints and crying and whining	(Yiddish) a nagging complaint
	(Yiddish) a constant complainer

complainer (verb)	kvetch (verb)
	express complaints, discontent, displeasure, or unhappiness