What is the meaning of the word "a-ok"?

Definitions:

Completely right or acceptable. ADJECTIVE
- I'm not a morning person, so I'm A-OK with working the night shift.
Operating or existing in perfect working order or in the best condition to be hoped for. adjective
- We've got the new engine fitted to the car now, and so far it's running A-OK.
Very definitely OK. ADJECTIVE
- I've felt A-OK since I left the hospital last week.
Very well or fine. ADJECTIVE
- The doctor says I'm A-OK now, that there's absolutely nothing wrong with me.