PERFIDIOUS
punic, perfidious, treacherous
(adjective) tending to betray; especially having a treacherous character as attributed to the Carthaginians by the Romans; “Punic faith”; “the perfidious Judas”; “the fiercest and most treacherous of foes”; “treacherous intrigues”
Source: WordNet® 3.1
Etymology
Adjective
perfidious (comparative more perfidious, superlative most perfidious)
Of, pertaining to, or representing perfidy; disloyal to what should command one's fidelity or allegiance. [from late 16th c.]
Synonyms
• (disloyal): disloyal, traitorous, treacherous, unfaithful
Source: Wiktionary
Per*fid"i*ous, a. Etym: [L. perfidious.]
1. Guilty of perfidy; violating good faith or vows; false to trust or
confidence reposed; teacherous; faithless; as, a perfidious friend.
Shak.
2. Involving, or characterized by, perfidy. "Involved in this
perfidious fraud." Milton.
Source: Webster’s Unabridged Dictionary 1913 Edition