ge·rah /ˈgɪrə/
  Ge·rah n.  Jewish Antiq. A small coin and weight; 1-20th of a shekel.
  Note: ☞ The silver gerah is supposed to have been worth about three cents; the gold about fifty-four cents; the weight equivalent to about thirteen grains.
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  Gerah
     a bean, probably of the carob tree, the smallest weight, and
     also the smallest piece of money, among the Hebrews, equal to
     the twentieth part of a shekel (Ex. 30:13; Lev. 27:25; Num.
     3:47). This word came into use in the same way as our word
     "grain," from a grain of wheat.