The Collaborative International Dictionary of English v.0.48:

Milreis \Mil"reis`\, n. [Pg. mil reis, i. e., one thousand reis;
   mil a thousand + reis, pl. of real a rei.]
   A Portuguese money of account rated in the treasury
   department of the United States at one dollar and eight
   cents; also, a Brazilian money of account rated at fifty-four
   cents and six mills (1913).
   [1913 Webster]

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

MIL-REIS. The name of a coin. The mil-reis of Portugal is taken as money of
account, at the custom-house, to be of the value of one hundred and twelve
cents. Act of March 13, 1843.
     2. The mil-reis of Azores, is deemed of the value of eighty-three and
one-third cents. Act of Match 3, 1843.
     3. The mil-reis of Madera, is deemed of the value of one hundred
cents. Id.