from The American Heritage® Dictionary of the English Language, 4th Edition
- interj. Used before the name of or a pronoun referring to a person or thing being formally addressed: "How can I put it to you, O you who prepare to travel with important matters on your mind?” ( Jo Durden-Smith).
- interj. Used to express surprise or strong emotion: "O how I laugh when I think of my vague indefinite riches” ( Henry David Thoreau).
- The symbol for the element oxygen.
- abbr. Baseball out
- abbr. outstanding
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The fifteenth letter of the basic modern Latin alphabet.
- n. Symbol for oxygen.
- n. The upper bound function also known as big O.
- prep. The English vocative particle (always in upper case), used for direct address in translations from languages which have the vocative case.
- interj. Expression of earnestness or reverence, used before the name of a deity or revered person in impassioned speech.
- n. The fifteenth letter of the English alphabet, called o and written in the Latin script.
- abbr. The number of overs bowled
- n. A blood type that lacks A or B antigens and may only receive transfusions of similar type O blood, but may donate to all (neglecting Rh factor). Synonym: universal donor.
- n. American Library Association Abbreviation of octavo, a book size (20-25 cm).
- n. Someone associated with Leyton Orient Football Club, as a player, coach, supporter etc.
- n. The ordinal number fifteenth, derived from this letter of the English alphabet, called o and written in the Latin script.
Old Saxon gloss o (950s) in Lambeth ms. (957) of Gallican Psalter and ó, o (>1000) in Durham Hymns, regularly as redundant "o eala þu" and "ó eala þu" at uppercase proper names in paraphrase and some verbs in periphrase; Anglo-Norman O (~1200) in mss. of Sts. Juliana and Katherine, and other religiose writs; and English O, o (~1525) in The New Testament Translation by William Tyndale for Ancient Greek ὦ, Latin o (vocative, intensive: Old English èalà, æàlà, ǽlà, hèlà; also Middle English O (Actus 13:10; Romayns 9:20; Galaþies 3:1), ò (Romayns 2:1,3), Irish a (Maþeu 15:28;17:17; Luk 9:41;24:25; Actus 13:10) or A (Actus 27:21; Romayns 11:33)—sometimes mistranscribed as O in online bibles—, þou (1Tymoþe 6:20), ȝe (Actus 18:14), or ∅ (Actus 1:1; Ebrews 10:7) in Newe Testament by Iohn Wiclif (1382). intensive, interrogative: Old English là; English lo, oh (1534)) (Wiktionary)