Source : Webster's Revised Unabridged Dictionary (1913)

Underplay \Un`der*play"\, v. i.
   1. To play in a subordinate, or in an inferior manner; to
      underact a part.

   2. (Card Playing) To play a low card when holding a high one,
      in the hope of a future advantage.

Underplay \Un"der*play`\, n. (Card Playing)
   The act of underplaying.

Source : WordNet®

underplay
     v 1: act (a role) with great restraint [syn: {underact}] [ant: {overact}]
     2: play a card lower than (a held high card)