Lewis Short
(adjective) : formīdābĭlĭs, e, 1. formido
* Causing fear, terrible, formidable (poet. and in post-class. prose; cf. formidolosus): lumen,Ov. M. 2, 857: nec formidabilis ulli,id. ib. 2, 174: Orcus,id. ib. 14, 116: aspectus,Gell. 14, 4, 2: sonus,id. 19, 1, 17: dolores et metus, per se formidabiles res,Sen. Ep. 123, 14.—In the neutr. adverbially: formidabile ridens,Stat. Th. 8, 582.
Charlton T. Lewis, Charles Short, A Latin Dictionary