Lewis Short
Ŏpĭter (noun M) : (cf. Prisc. p. 695 P.;
* Gen. Opetris; cf. Borghes. Framm. de' Fasti Cons. 1, p. 66), m. ob-pater, a Roman proenomen: Opiter est, cujus pater avo vivo mortuus est,Fest. p. 184 Müll.: Opiter Verginius,Liv. 2, 17; 2, 54.
Charlton T. Lewis, Charles Short, A Latin Dictionary