vary vs variation

vary is not a noun while variation is a noun.

Word	Noun	Adjective	Verb	Adverb
vary	No	No	Yes	No
variation	Yes	No	No	No

vary (noun)	variation (noun)
	an activity that varies from a norm or standard
	the act of changing or altering something slightly but noticeably from the norm or standard
	(ballet) a solo dance or dance figure
	an artifact that deviates from a norm or standard
	something a little different from others of the same type
	a repetition of a musical theme in which it is modified or embellished
	an instance of change; the rate or magnitude of change
	(biology) an organism that has characteristics resulting from chromosomal alteration
	(astronomy) any perturbation of the mean motion or orbit of a planet or satellite (especially a perturbation of the earth's moon)
	the process of varying or being varied
	the angle (at a particular location) between magnetic north and true north

vary (verb)	variation (verb)
become different in some particular way, without permanently losing one's or its former characteristics or essence
make something more diverse and varied
be at variance with; be out of line with
be subject to change in accordance with a variable