warn vs say

warn is not a noun while say is a noun.

Word	Noun	Adjective	Verb	Adverb
warn	No	No	Yes	No
say	Yes	No	Yes	No

As verbs, say is a hypernym of warn; that is, say is a word with a broader meaning than warn:

Other hypernyms of warn include enjoin, order, tell.

warn (noun)	say (noun)
	the chance to speak

warn (verb)	say (verb)
notify of danger, potential harm, or risk	express in words
advise or counsel in terms of someone's behavior	report or maintain
notify, usually in advance	speak, pronounce, or utter in a certain way
ask to go away	express a supposition
	give instructions to or direct somebody to do something with authority
	communicate or express nonverbally
	recite or repeat a fixed text
	indicate
	state as one's opinion or judgement; declare
	utter aloud
	have or contain a certain wording or form