/oh/ , interj., n., pl. O's .
1. (used before a name in direct address, esp. in solemn or poetic language, to lend earnestness to an appeal): Hear, O Israel!
2. (used as an expression of surprise, pain, annoyance, longing, gladness, etc.)
3. the exclamation "O."
[ 1125-75; ME o ]
2. Gram. object.
1. the fifteenth in order or in a series.
2. the Arabic cipher; zero.
3. ( sometimes l.c. ) the medieval Roman numeral for 11. Cf. Roman numerals .
4. Physiol. a major blood group, usually enabling a person whose blood is of this type to donate blood to persons of group O, A, B, or AB and to receive blood from persons of group O. Cf. ABO system .
5. Chem. oxygen.
6. Logic. See particular negative .