- (a.) One.
- (n.) A cipher; zero.
- (n.) Something shaped like the letter O; a circle or oval.
- Among the ancients, O was a mark of triple time, from the notion that the ternary or number 3, is the most perfect of numbers, and properly expressed by a circle, the most perfect figure.
- (n.) The letter O or its sound.
- (interj.) An exclamation used in calling or directly addressing a person or personified object; also, as an emotional or impassioned exclamation expressing pain, grief, surprise, desire, fear, etc.
- O, the fifteenth letter of the English alphabet, derives its form, value, and name from the Greek O, through the Latin. The letter came into the Greek from the Ph/nician, which possibly derived it ultimately from the Egyptian. Etymologically, the letter o is most closely related to a, e, and u; as in E. bone, AS. ban; E. stone, AS. stan; E. broke, AS. brecan to break; E. bore, AS. beran to bear; E. dove, AS. d/fe; E. toft, tuft; tone, tune; number, F. nombre.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). o. Retrieved September 21, 2026, from http://smartdefine.org/o/definitions/2037810 |
| Chicago | Webster's. 2011. "o" http://smartdefine.org/o/definitions/2037810 (accessed September 21, 2026). |
| Harvard | Webster's 2011, o, Smart Define, viewed 21 September, 2026, <http://smartdefine.org/o/definitions/2037810>. |
| MLA | Webster's. "o" 27 May 2011. Web. 21 September 2026. <http://smartdefine.org/o/definitions/2037810> |