Source : Webster's Revised Unabridged Dictionary (1913)

Underhand \Un"der*hand`\, a.
   1. Secret; clandestine; hence, mean; unfair; fraudulent.
      --Addison.

   2. (Baseball, Cricket, etc.) Done, as pitching, with the hand
      lower than the shoulder, or, as bowling, with the hand
      lower than elbow.

Underhand \Un"der*hand`\, adv.
   1. By secret means; in a clandestine manner; hence, by fraud;
      unfairly.

            Such mean revenge, committed underhand. --Dryden.

            Baillie Macwheeble provided Janet, underhand, with
            meal for their maintenance.           --Sir W.
                                                  Scott.

   2. (Baseball, Cricket, etc.) In an underhand manner; -- said
      of pitching or bowling.

Source : WordNet®

underhand
     adv 1: slyly and secretly; "Mean revenge, committed underhand"-
            John Donne; "oldline aristocratic diplomats
            underhandedly undermined the attempt...to align
            Germany with the Western democracies"- C.G.Bowers
            [syn: {underhandedly}]
     2: with the hand swung below shoulder level'; "throwing a ball
        underarm" [syn: {underarm}]

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