Lewis Short
(adjective) : insĭdĭōsus, a, um, insidiae
* Cunning, artful, deceitful, dangerous, insidious (class.).
* Of persons: quis insidiosior unquam fuit?Cic. Verr. 2, 2, 78, § 192.
* Of inanim. and abstr. things: Capraria insidiosa naufragiis,Plin. 3, 5, 11, § 78: pocula Circes,Ov. M. 14, 294: verba,id. H. 20, 212: clementia,Cic. Att. 8, 16, 2. — Sup., Plin. 29, 1, 8, § 28. — Adv.: insĭdĭōsē, cunningly, deceitfully, insidiously: in gratiam rediit cum illo,Cic. Rab. Post. 12, 33: me insidiosissime tractavit,id. Q. Fr. 1, 3, 8.
Charlton T. Lewis, Charles Short, A Latin Dictionary