Lewis & Short

Ŏpĭter, ĭtĕris and ĭtris (cf. Prisc. p. 695 P.; gen. Opetris; cf. Borghes. Framm. deFasti Cons. 1, p. 66), m. [ob-pater], a Roman prœnomen: Opiter est, cujus pater avo vivo mortuus est, Fest. p. 184 Müll.: Opiter Verginius, Liv. 2, 17; 2, 54.