stammer vs verbalize

stammer is a noun but verbalize is not a noun.

Word	Noun	Adjective	Verb	Adverb
stammer	Yes	No	Yes	No
verbalize	No	No	Yes	No

As verbs, verbalize is a hypernym of stammer; that is, verbalize is a word with a broader meaning than stammer:

Other hypernyms of stammer include mouth, speak, talk, utter, verbalise.

stammer (noun)	verbalize (noun)
a speech disorder involving hesitations and involuntary repetitions of certain sounds

stammer (verb)	verbalize (verb)
speak haltingly	convert into a verb
	express in speech
	be verbose
	articulate; either verbally or with a cry, shout, or noise