Lewis & Short

2. prō (less correctly prōh), interj., an exclamation of wonder or lamentation, O! Ah! Alas! (class.).

        1. (α) With nom.: proh! bonae frugi hominem te jam pridem esse arbitror, Plaut. Cas. 2, 4, 4: pro Juppiter! Enn. ap. Varr L. L. 7, § 12 Müll. (Trag. v 225 Vahl.); Ter. And. 4, 3, 17; id. Eun. 3, 5, 2; id. Ad. 1, 2, 31; cf.: pro supreme Juppiter, id. ib. 2, 1, 42: pro Juppiter, Hominis stultitiam! id. ib. 3, 3, 12: pro di immortales, id. ib. 3, 4, 1; cf.: pro, dii immortales: Cic. Imp. Pomp. 12, 33: pro curia inversique mores! Hor. C. 3, 5, 7: pro scelus, Mart. 2, 46, 8.
        2. (β) Parenthet.: pro, quanta potentia regni Est, Venus alma, tui, Ov. M. 13, 758: et mea, pro! nullo pondere verba cadunt, id. H. 3, 98: tantum, pro! degeneramus a patribus, Liv. 22, 14, 6; Curt. 4, 16, 10.
        3. (γ) With acc.: pro divom fidem! Enn. ap. Don. ad. Ter. Phorm. 2, 2, 25 (Sat. v. 30 Vahl.); Ter. Ad. 4, 7, 28; cf.: pro deum atque hominum fidem! id. And. 1, 5, 2; 11; id. Heaut. 1, 1, 9; Cic. Tusc. 5, 16, 48; instead of which, ellipt.: pro deum immortalium! Ter. Phorm. 2, 3, 4: pro deum atque hominum, id. Hec. 2, 1, 1: pro fidem deum! facinus foedum, id. Eun. 5, 4, 21.
        4. (δ) With gen.: pro malae tractationis! Tert. Poen. fin.