okay vs o.k.

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

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

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

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

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

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

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

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