Lewis Short
(adjective) : spontānĕus, a, um, sponte
* Of one's free will, voluntary, spontaneous (late Lat.): mors,Macr. Somn. Scip. 2, 22: voluntas,free will,Cod. Just. 2, 3, 2: benignitates numinum,Arn. 3, p. 114.—Adv.: spontānĕē, voluntarily, willingly, of one's own mind: apparere tumores,Theod. Prisc. 1, 8; Vulg. 1 Pet. 5, 2; Hier. Ep. 52, n. 7.
Charlton T. Lewis, Charles Short, A Latin Dictionary