The Collaborative International Dictionary of English v.0.48:

Pistareen \Pis`ta*reen"\, n.
   An old Spanish silver coin of the value of about twenty
   cents.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

PISTAREEN. A small Spanish coin. It is not a coin made current by the laws
of the United States. 10 Pet. 618.