Source : Webster's Revised Unabridged Dictionary (1913)

   5. (Chess) One of the superior men, distinguished from a
      pawn.

   6. A castle; a fortified building. [Obs.] --Spenser.

   {Of a piece}, of the same sort, as if taken from the same
      whole; like; -- sometimes followed by with. --Dryden.

   {Piece of eight}, the Spanish piaster, formerly divided into
      eight reals.

   {To give a piece of one's mind to}, to speak plainly,
      bluntly, or severely to (another). --Thackeray.

   {Piece broker}, one who buys shreds and remnants of cloth to
      sell again.

   {Piece goods}, goods usually sold by pieces or fixed
      portions, as shirtings, calicoes, sheetings, and the like.

Source : WordNet®

piece of eight
     n : an old silver Spanish coin; worth 8 reales