for certain vs colloquialism

for certain is not a noun while colloquialism is a noun.

Word	Noun	Adjective	Verb	Adverb
for certain	No	No	No	Yes
colloquialism	Yes	No	No	No

for certain (noun)	colloquialism (noun)
	a colloquial expression; characteristic of spoken or written communication that seeks to imitate informal speech

for certain (adverb)	colloquialism (adverb)
definitely or positively (`sure' is sometimes used informally for `surely')