(adjective) : perfĭdĭōsus, a, um, perfidia
* Faithless, dishonest, treacherous, false, perfidious (class.).
* Of persons: fallax, perfidiosus,Cic. Pis. 27, 66: perfidiosus et subdolus animo,Tac. A. 16, 32.—Sup.: omnium perfidiosissimus,Cic. N. D. 3, 32, 80.
* Of inanim. and abstr. things: amor,Plaut. Cist. 1, 1, 73: nihil perfidiosum et insidiosum et fallax in amicitiā,Cic. Fam. 3, 10, 7; id. Rosc. Com. 6, 16.—Adv.: per-fĭdĭōsē, faithlessly, dishonestly, treacherously, perfidiously (rare but class.): hercle istam rem judicasti perfidiose,Plaut. Curc. 5, 3, 41: multa perfidiose facta,Cic. Rosc. Am. 40, 118: perfidiose, crudeliter factum,Auct. Her. 1, 5, 8.—Comp.: perfidiosius rebellantes,Suet. Aug. 21.

s. TLL