gaffe vs blunder

gaffe and blunder both are nouns.

Word	Noun	Adjective	Verb	Adverb
gaffe	Yes	No	No	No
blunder	Yes	No	Yes	No

As nouns, blunder is a hypernym of gaffe; that is, blunder is a word with a broader meaning than gaffe:

Other hypernyms of gaffe include bloomer, blooper, boner, boo-boo, botch, bungle, flub, foul-up, fuckup, pratfall.

gaffe (noun)	blunder (noun)
a socially awkward or tactless act	an embarrassing mistake

gaffe (verb)	blunder (verb)
	utter impulsively
	make one's way clumsily or blindly
	commit a faux pas or a fault or make a serious mistake