Lewis Short
dē-nīgro, āre
* V. a., to blacken utterly, dye or color very black (very rare; in the Ciceron. per. not at all).
* Lit.: terram (amurca),Varr. R. R. 1, 55 fin.: lanam,Plin. 33, 6, 35, § 109: capillum,id. 23, 5, 53, § 99: faciem super carbones,Vulg. Thren. 4, 8.— *
* Trop.: honorem famamque alicujus, to blacken, i. e. to asperse, defame, Firm. 5, 10 fin.
Charlton T. Lewis, Charles Short, A Latin Dictionary