malcontent vs quibbler

malcontent and quibbler both are nouns.

Word	Noun	Adjective	Verb	Adverb
malcontent	Yes	Yes	No	No
quibbler	Yes	No	No	No

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

malcontent: a person who is discontented or disgusted
quibbler: a disputant who quibbles; someone who raises annoying petty objections

Other hyponyms of malcontent include caviler, caviller, pettifogger, sorehead, squabbler.

malcontent (noun)	quibbler (noun)
a person who is discontented or disgusted	a disputant who quibbles; someone who raises annoying petty objections

malcontent (adjective)	quibbler (adjective)
discontented as toward authority