Okay (or OK, O.K.) is the most versatile colloquial English word.
As a noun (I need your OK) it means approval.
As an adjective (Lunch was OK) it means acceptable.
As an adverb (We did OK) it means adequately.
As a verb (Can you OK this for me?) it means consent.
As an interjection (Ok. I´ll do that) it means compliance, agreement (Shall we go? OK.) or great enthusiasm (OK!.) by using the appropriate voice tone.
The most widespread of all English words can also be used as a filler of space (Ok, can I have your attention, please?) or to seek confirmation (Is that OK?)
The Origin of OK
According to Bill Bryson (Mother Tongue The English Language, Penguin 1990) it became fashion in Boston and New York as a comic misspelling of Oll Korrect (OK) apparently used by President Andrew Jackson´s bad spelling. Coincidentally in 1840 supporters of President Martin Van Buren (Andrew Jackson´s protégé) founded an organization to help his campaign The Democratic O.K. Club. O.K. stood for Old kinderhook, a nickname for the democratic candidate who was a native of Old Kinderhook, New York.
Vote for OK sounded better than his Dutch name…