Source : Webster's Revised Unabridged Dictionary (1913)

Countermark \Coun"ter*mark`\ (-m?rk`), n.
   1. A mark or token added to those already existing, in order
      to afford security or proof; as, an additional or special
      mark put upon a package of goods belonging to several
      persons, that it may not be opened except in the presence
      of all; a mark added to that of an artificer of gold or
      silver work by the Goldsmiths' Company of London, to
      attest the standard quality of the gold or silver; a mark
      added to an ancient coin or medal, to show either its
      change of value or that it was taken from an enemy.

   2. (Far.) An artificial cavity made in the teeth of horses
      that have outgrown their natural mark, to disguise their
      age.

Countermark \Coun`ter*mark"\ (koun`t[~e]r*m[aum]rk"), v. t.
   To apply a countermark to; as, to countermark silverware; to
   countermark a horse's teeth.