(O’s, o’s)
1.
O is the fifteenth letter of the English alphabet.
N-VAR
2.
O is used to mean zero, for example when you are telling someone a telephone number, or mentioning a year such as 1908. (SPOKEN)
NUM
3.
O is used in exclamations, especially when you are expressing strong feelings. (LITERARY)
O how mistaken you are!...
O God, I want to go home.
EXCLAM feelings
see also oh