blunder vs stumble

blunder and stumble both are nouns.

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

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

blunder (noun)	stumble (noun)
an embarrassing mistake	an unsteady uneven gait
	an unintentional but embarrassing blunder

blunder (verb)	stumble (verb)
utter impulsively	make an error
make one's way clumsily or blindly	miss a step and fall or nearly fall
commit a faux pas or a fault or make a serious mistake	walk unsteadily, tripping repeatedly
	encounter by chance