impact vs stimulate

impact is a noun but stimulate is not a noun.

Word	Noun	Adjective	Verb	Adverb
impact	Yes	No	Yes	No
stimulate	No	No	Yes	No

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

impact (noun)	stimulate (noun)
influencing strongly
the violent interaction of individuals or groups entering into combat
the striking of one body against another
a forceful consequence; a strong effect

impact (verb)	stimulate (verb)
have an effect upon	cause to be alert and energetic
press or wedge together; pack together	act as a stimulant
	provide the needed stimulus for
	cause to do; cause to act in a specified manner
	cause to occur rapidly
	stir the feelings, emotions, or peace of
	stir feelings in