faithless
/ˈfāth-ləs/
adjective
not true to allegiance or duty : treacherous, disloyal
not to be relied on : untrustworthy
a faithless servant
faithless false disloyal traitorous treacherous perfidious mean untrue to what should command one's fidelity or allegiance. faithless applies to any failure to keep a promise or pledge or any breach of allegiance or loyalty. false stresses the fact of failing to be true in any manner ranging from fickleness to cold treachery.
noun
an elector who votes in the electoral college for a candidate other than the one who won the popular vote in the elector's state
The U.S. Supreme Court has unanimously upheld laws across the country that remove or punish rogue Electoral College delegates who refuse to cast their votes for the presidential candidate they were pledged to support. The decision Monday was a loss for "faithless electors," who argued that under the Constitution they have discretion to decide which candidate to support.