n. (also o) (pl. Os or O's)
1 the fifteenth letter of the alphabet.
2 (0) nought, zero (in a sequence of numerals esp. when spoken).
3 a human blood type of the ABO system.
2.
abbr. (also O.) Old.
3.
symb. Chem. the element oxygen.
4.
int.
1 var. of OH(1).
2 prefixed to a name in the vocative (O God).
Etymology: ME, natural excl.
Useful english dictionary. 2012.