Ruding (i. 187) states that in the Gentleman's Magazine for 1812 (p. 331) there is a communication from Dr. Pegge, who imagined that he had discovered the gold Penny of Henry III in a Jewish doc- ument under the name of Jaku. This he considers as equivalent to pure or sterling. The Jews, he says, " used Denarim and Jaku, just in the same manner as the Chris- tians applied their words Denarius and Sterlingus. "
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)