ō (long also before an initial vowel:
I o ego, Ov. M. 8, 51; Hor. A. P. 301; but also short: ŏ Alexi, Verg. E. 2, 65), interj. The commonest exclamation of joy, astonishment, desire, grief, indignation, etc.; O! Oh! constr. usually with voc. or acc.; less freq. with nom., gen., utinam, si.
1 With voc. : o Romule, Romule die, Enn. ap. Cic. Rep. 1, 41 Vahl. (Ann. v. 115 Vahl.): o Tite, tute Tati, id. ap. Prisc. p. 947 P. (Ann. v. 113 Vahl.); cf.: o Tite, si quid te adjuero, id. ap. Cic. Sen. 1, 1 (Ann. v. 339 Vahl.): o mi Furni! Cic. Fam. 10, 26, 2: o paterni generis oblite, id. Pis. 26, 62.—
2 With acc.: o faciem pulchram ... o infortunatum senem, Ter. Eun. 296 and 298: o miseras hominum mentes, Lucr. 2, 14: o me perditum, o me afflictum! Cic. Fam. 14, 4, 3: o hominem nequam! id. Att. 4, 13, 2: o praeclarum custodem ovium, ut aiunt, lupum! id. Phil. 3, 11, 27: o rem totam odiosam, id. Att. 6, 4, 1: o Bruti amanter scriptas, litteras, id. ib. 15, 10.—
3 With nom. (rare): o pietas animi, Enn. ap. Cic. Ac. 2 ( Luc. ), 27, 88 (Ann. v. 8 Vahl.): o Patricoles, id. ap. Cic. Tusc. 2, 16, 38 (Trag. v. 14 Vahl.): o vir fortis atque amicus! Ter. Phorm. 324: o ego ter felix, Ov. M. 8, 51; so, o ego, Hor. A. P. 301: o multum miseri, Ov. M. 4, 155: o qualis facies! Juv. 10, 157.—
4 With utinam : o utinam Obrutus esset! Ov. H. 1, 5; id. M. 1, 363 al.—
5 With si : quamquam, o si solitae quicquam virtutis adesset! yet oh! if , etc., Verg. A. 11, 415.—
6 With gen.: o nuntii beati, Cat. 9, 5.—By poets also placed after a word: o lux Dardaniae, spes o fidissima Teucrūm, Verg. A. 2, 281: quid o tua fulmina cessant! Ov. M. 2, 279.—Three times repeated: o pater, o genitor, o sanguen dis oriundum, Enn. ap. Cic. Rep. 1, 41 (Ann. v. 117 Vahl.); cf.: o pater, o patria, o Priami domus, id. ap. Cic. Tusc. 3, 19, 44 (Trag. v. 118 Vahl.): o soror, o conjux, o femina sola superstes, Ov. M. 1, 351.