adj. 25B6; adjective (poetic/literary) TREACHEROUS, duplicitous, deceitful, disloyal, faithless, unfaithful, traitorous, treasonous, false, false-hearted, double-dealing, two-faced, untrustworthy.
faithful.
PERFIDIOUS
Meaning of PERFIDIOUS in English
Concise Oxford thesaurus English vocabulary. Краткий оксфордский словарь английского языка тезаурус. 2012