stammer vs speak

stammer is a noun but speak is not a noun.

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

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

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

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

stammer (verb)	speak (verb)
speak haltingly	express in speech
	exchange thoughts; talk with
	use language
	give a speech to
	make a characteristic or natural sound