(adjective) : perfĭdus, a, um, per-fides
* That breaks his promise, faithless, false, dishonest, treacherous, perfidious.
* Lit. (class.; syn. infidus): vanum et perfidiosum esse,Cic. Quint. 6, 26: omnes, aliud agentes, aliud simulantes, perfidi, improbi, malitiosi sunt,id. Off. 3, 14, 60.
* With gen. (poet.): gens perfida pacti,faithless,Sil. 1, 5.
* Transf., treacherous, unsafe, dangerous (poet. and in post-class. prose): freta,Sen. Med. 302: saxa,id. Agam. 570: perfidum glacie flumen,Flor. 3, 4, 5: perfida et lubrica via,Prop. 4 (5), 4, 49. vappa,wretched wine that has a good appearance,Mart. 12, 48, 14.—Sup.: homo, quoad vixerat, perfidissimus,Amm. 16, 12, 25.—Adv.: perfĭ-dē, faithlessly, perfidiously, treacherously (post-Aug.): perfide recuperans,Sen. Contr. 4, 26: rumpere pactum,Gell. 20, 1, 54: agere,Dig. 26, 7, 55: quod perfide gestum est,ib. 44, 4, 4, § 13.
* Adverb.: perfidum ridens Venus (= maligne ac dolose), Hor. C. 3, 27, 67.—As subst.: perfĭdus, i, m., a scoundrel, Juv. 13, 245; 9, 82.

s. TLL