perfidus

From per (“through, along”) +‎ fidēs (“faith; trust”) +‎ -us (adjectival suffix), based on the phrase per fidem dēcipere[1]

• (Classical) IPA^(key): /ˈper.fi.dus/, [ˈpɛrfɪd̪ʊs̠]
• (modern Italianate Ecclesiastical) IPA^(key): /ˈper.fi.dus/, [ˈpɛrfid̪us]

perfidus (feminine perfida, neuter perfidum); first/second-declension adjective

1. that breaks his promise, false, faithless, dishonest, disloyal, treacherous, perfidious, deceitful, traitorous
   • 29 BCE – 19 BCE, Virgil, Aeneid 4.305–306:

     “Dissimulāre etiam spērāstī, perfide, tantum
     posse nefās, tacitusque meā dēcēdere terrā?”

     “Had you even hoped to be able to hide so great a crime – you faithless [man]! – and to slip away from my land unnoticed?”
     (Dido had believed that she and Aeneas shared a commitment, and yet he and the Trojans are preparing to leave Carthage. Translators Shadi Bartsch, Robert Fagles, Stanley Lombardo, Sarah Ruden, and David West supply the noun “traitor”. Frederick Ahl (Oxford, 2007) translates “perfide” as “you perfidious cheat”, and footnotes the irony that ancient Romans reputed the Carthaginians as being perfidious.)

2. (by extension) treacherous, unsafe, dangerous

   Synonym: īnfīdus

First/second-declension adjective.

• (antonym(s) of “faithless”): castus, honestus, pudīcus

• perfidē
• perfidia

• perfidiōsē
• perfidiōsus

• French: perfide
  • German: perfide
• Italian: perfido
• Portuguese: pérfido
• Spanish: pérfido

• “perfidus”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
• “perfidus”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
• perfidus in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.