Lewis Short
(adjective) : sŏnĭ-pēs (sŏnŭpēs), pĕdis, sonus
* With sounding feet, noisy-footed (poet.): turba (in Isidis sacris),Grat. Cyn. 43.—As subst., noisy-foot, i. e. a horse, a prancer, steed: fremit aequore toto Insultans sonipes et pressis pugnat habenis,Verg. A. 11, 600; Cat. 63, 41; Sil. 1, 222; Val. Fl. 3, 334; Stat. Th. 5, 3 al. (in Cic., sonipedes is cited as an example of a fourth paeon, de Or. 3, 47, 183).
Charlton T. Lewis, Charles Short, A Latin Dictionary