Source : Webster's Revised Unabridged Dictionary (1913)

Coin \Coin\ (koin), n. [F. coin, formerly also coing, wedge,
   stamp, corner, fr. L. cuneus wedge; prob. akin to E. cone,
   hone. See {Hone}, n., and cf. {Coigne}, {Quoin},
   {Cuneiform}.]
   1. A quoin; a corner or external angle; a wedge. See
      {Coigne}, and {Quoin}.

   2. A piece of metal on which certain characters are stamped
      by government authority, making it legally current as
      money; -- much used in a collective sense.

            It is alleged that it [a subsidy] exceeded all the
            current coin of the realm.            --Hallam.

   3. That which serves for payment or recompense.

            The loss of present advantage to flesh and blood is
            repaid in a nobler coin.              --Hammond.

   {Coin balance}. See Illust. of {Balance}.

   {To pay one in his own coin}, to return to one the same kind
      of injury or ill treatment as has been received from him.
      [Colloq.]