o.k. vs okay

o.k. is not a noun while okay is a noun.

Word	Noun	Adjective	Verb	Adverb
o.k.	No	Yes	No	No
okay	Yes	Yes	Yes	Yes

As adjectives, o.k. and okay are synonyms defined as:

Other synonyms of o.k. include all right, cool, fine, hunky-dory, ok.

o.k. (noun)	okay (noun)
	an endorsement

o.k. (adjective)	okay (adjective)
being satisfactory or in satisfactory condition	being satisfactory or in satisfactory condition

o.k. (verb)	okay (verb)
	give sanction to

o.k. (adverb)	okay (adverb)
	in a satisfactory or adequate manner