nitpicker vs critic

nitpicker and critic both are nouns.

Word	Noun	Adjective	Verb	Adverb
nitpicker	Yes	No	No	No
critic	Yes	No	No	No

As nouns, critic is a hypernym of nitpicker; that is, critic is a word with a broader meaning than nitpicker:

nitpicker: someone who makes small and unjustified criticisms
critic: someone who frequently finds fault or makes harsh and unfair judgments

nitpicker (noun)	critic (noun)
someone who makes small and unjustified criticisms	a person who is professionally engaged in the analysis and interpretation of works of art
	anyone who expresses a reasoned judgment of something
	someone who frequently finds fault or makes harsh and unfair judgments