WordWeb Online

1. Involving deception
   "deceitful advertising"; "smooth, shining, and deceitful as thin ice";
   - fallacious, fraudulent
    
2. Marked by deliberate deceptiveness especially by pretending one set of feelings and acting under the influence of another
   "she was a deceitful scheming little thing";
   - ambidextrous, double-dealing, duplicitous, Janus-faced, two-faced, double-faced, double-tongued

See also: dishonest, dishonorable [US], dishonourable [Brit, Cdn]

Encyclopedia: Deceitful