underhanded

/ˈʌndərˌhændɪd/
adjective
  1. Done in a secret, dishonest, or unfair way; same as 'underhand'.
    • The company used underhanded methods to spy on its competitors.
    • His underhanded trick caused his friend to lose the game.
    • I was shocked by her underhanded attempt to steal the credit.
Antonyms