really vs intensifier

really is not a noun while intensifier is a noun.

Word	Noun	Adjective	Verb	Adverb
really	No	No	No	Yes
intensifier	Yes	No	No	No

really (noun)	intensifier (noun)
	a modifier that has little meaning except to intensify the meaning it modifies

really (adverb)	intensifier (adverb)
used to give emphasis
in fact (used as intensifiers or sentence modifiers)
in accordance with truth or fact or reality
in actual fact