8. (adv.)OK all right; well enough; successfully; fine: He sings OK.
9. OK (used to request or express agreement, acknowledgment, approval, etc.)
10. (n.)OK an approval, agreement, or endorsement.
11. (v.t.)OK to endorse or indicate approval of; authorize.
Etymology: (initials of a facetious folk phonetic spelling, e.g., oll or orl korrect representing all correct, first attested in Boston in 1839, then used in 1840 by Democrat partisans of Martin Van Buren, who allegedly named their organization, the O.K. Club, in allusion to the initials of Old Kinderhook, Van Buren's nickname, derived from his birthplace, Kinderhook, New York)
Definition of 'OK'
Princeton's WordNet
1. (noun)Oklahoma, Sooner State, OK a state in southcentral United States
2. (adj)O.K., OK, okay, okey, okeh an endorsement "they gave us the O.K. to go ahead"
3. (adverb)all right, fine, o.k., ok, okay, hunky-dory being satisfactory or in satisfactory condition "an all-right movie"; "the passengers were shaken up but are all right"; "is everything all right?"; "everything's fine"; "things are okay"; "dinner and the movies had been fine"; "another minute I'd have been fine"
Definitions of OK 
