two-timing vs underhanded

two-timing

• Sexually or romantically unfaithful. 

• The practice of being sexually or romantically unfaithful. 

underhanded

• Secret; surreptitious. 

• Done by moving the hand (and arm) from below. 

• Sly, dishonest, corrupt, cheating. 

• Insincere; sarcastic. 

• An underhanded compliment is actually criticism. 

• His underhanded trick backfired and he was disqualified. 

• Understaffed. 

• In an underhanded manner. 

• Devious people, collectively.