Lewis Short
(adjective) : implăcĭdus (inpl-), a, um, 2. in-placidus
* Ungentle, rough, savage, fierce (poet.): Genauni, implacidum genus,Hor. C. 4, 14, 10: Mars divum implacidissimus,Stat. Th. 9, 4: implacido letalis Sirius igni,Stat. S. 2, 1, 216: fores,Prop. 4 (5), 9, 14. cornu,Stat. Th. 5, 199.
Charlton T. Lewis, Charles Short, A Latin Dictionary