The popular informal word ‘OK’ is a capitalised word except when written as ‘okay’.
According to etymonline.com, “…the abbreviation is of ‘oll korrect.’ Probably further popularized by use as an election slogan by the O.K. Club, New York boosters of Democratic president Martin Van Buren’s 1840 re-election bid, in allusion to his nickname Old Kinderhook…”
- It’s OK to be angry at such inhuman behaviour.
- OK, OK, I understand.
- It’s okay to cry when you are happy.