See Also:

O(1) (iou)



O, o.
The fifteenth letter of the modern English alphabet and the fourteenth of the ancient Roman one, corresp. to Greek o, repr. the sixteenth letter of the Phoenician and ancient Semitic alphabet. The sound orig. represented by the letter was probably a mid-back rounded or labial vowel. For its principal mod. sounds see the Key to the Pronunciation. Pl. oes, O's, Os.
I.
The letter and its sound.
The shape of the letter.
O-ring a gasket or seal (usu. of rubber) in the form of a ring with a circular cross-section.
II. Symbolical uses.
Used to denote serial order; applied e.g. to the fifteenth (or fourteenth, I or J being omitted) group or section, sheet of a book, etc.
Logic. (Cap. O.) A particular negative proposition.
(Cap. O.) The blood group characterized by the absence of both the A and B agglutinogens.
III.
Abbrevs.: O = Ohio; old; ordinary (in O level (Hist.), of the General Certificate of Education examination); oxygen.