The Collaborative International Dictionary of English v.0.48:

Rouble \Rou"ble\, n.
   A coin. See Ruble.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rouble
    n 1: the basic unit of money in Russia [syn: ruble, rouble]

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

ROUBLE. The name of a coin. The rouble of Russia, as money of account, is
deemed and taken at the custom-house, to be of the value of seventy-five
cents. Act March 3, 1843.