perfidiousness perfidiously • perfidy · · · Info · Definitions · Synonyms · Characters · · perfidiousness · · Text Latin · · Script 14 · · Length Definitions · · · (noun) betrayal of a trust. Synonyms: perfidy, treachery. · · Noun Definition 1 Synonyms · · · perfidy · · Synonym 1 treachery · · Synonym 2 Characters · · d latin small letter d U+0064 e latin small letter e U+0065 f latin small letter f U+0066 i latin small letter i U+0069 n latin small letter n U+006E o latin small letter o U+006F p latin small letter p U+0070 r latin small letter r U+0072 s latin small letter s U+0073 u latin small letter u U+0075