O.K.

nouns

an endorsement
"they gave us the O.K. to go ahead"
O.K., OK, okay, okeh, okey

verbs

give sanction to
"I approve of his educational policies"
O.K., approve, okay, sanction
is derived from
OK

adverbs

in a satisfactory or adequate manner
"she'll do okay on her own"; "held up all right under pressure"; (`alright' is a nonstandard variant of `all right')
O.K., all right, alright, okay