Source : Webster's Revised Unabridged Dictionary (1913)

Underhanded \Un"der*hand`ed\, a.
   1. Underhand; clandestine.

Source : WordNet®

underhanded
     adj 1: marked by deception; "achieved success in business only by
            underhand methods" [syn: {sneaky}, {underhand}]
     2: with hand brought forward and up from below shoulder level;
        "an underhand pitch"; "an underhand stroke" [syn: {underhand},
         {underarm}] [ant: {overhand}]