The Collaborative International Dictionary of English v.0.48:

Picaroon \Pic`a*roon"\, n. [Sp. picaron, aug. of picaro roguish,
   n., a rogue.]
   One who plunders; especially, a plunderer of wrecks; a
   pirate; a corsair; a marauder; a sharper. --Sir W. Temple.
   [1913 Webster]