Lewis & Short

oxymōrus, a, um, adj., = ὀξύμωρος, acutely silly: oxymora verba, expressions which at first sight appear absurd, but which contain a concealed point; so especially of such apparently contradictory assertions as: cum tacent clamant, etc. (Cic. Cat. 1, 8, 21), Pseudo Ascon. ad Cic. Div. in Caecil. 1.