Lewis Short
(verb) : nīgrĕo, ēre, 1. niger
* To be black (ante-class.): solis occasu nigret, Pac. ap. Non. 144, 11 (Trag. Rel. v. 88 Rib.): nimbis nigret, opp. splendet,Att. ib. 13 (Trag. Rel. v. 260 Rib.).
Charlton T. Lewis, Charles Short, A Latin Dictionary