disloyal
Definitions
Failing to be loyal to a person, country, or organization to which one has obligations.
Characterized by or showing a lack of allegiance or faithfulness.
Examples
He felt that betraying his business partner was a disloyal act that ruined their long-standing friendship.
The king punished the knight for being disloyal to the crown during the rebellion.
Synonyms
treacherous unfaithful traitorous faithless perfidious false untrustworthy