err vs stumble

err is not a noun while stumble is a noun.

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

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

Other hyponyms of err include misremember, slip up, trip up, misjudge, fall for.

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

err (verb)	stumble (verb)
to make a mistake or be incorrect	make an error
wander from a direct course or at random	miss a step and fall or nearly fall
	walk unsteadily, tripping repeatedly
	encounter by chance