Lewis Short
mītĭgātĭo (noun F) : mitigo
* A soothing, mitigating, mitigation (rare but class.), Cic. de Or. 3, 30, 118: multis mitigationibus lenire,Auct. Her. 4, 37, 49: quae non indiget mitigationis,id. ib. 4, 37, 50: si est lingua curationis, est et mitigationis,Vulg. Sir. 36, 25.
Charlton T. Lewis, Charles Short, A Latin Dictionary