stimulation vs natural action

stimulation and natural action both are nouns.

Word	Noun	Adjective	Verb	Adverb
stimulation	Yes	No	No	No
natural action	Yes	No	No	No

As nouns, natural action is a hypernym of stimulation; that is, natural action is a word with a broader meaning than stimulation:

stimulation: (physiology) the effect of a stimulus (on nerves or organs etc.)
natural action: a process existing in or produced by nature (rather than by the intent of human beings)

Other hypernyms of stimulation include action, activity, natural process.

stimulation (noun)	natural action (noun)
the act of arousing an organism to action	a process existing in or produced by nature (rather than by the intent of human beings)
mutual sexual fondling prior to sexual intercourse
any stimulating information or event; acts to arouse action
(physiology) the effect of a stimulus (on nerves or organs etc.)