Source : Webster's Revised Unabridged Dictionary (1913)

Loophole \Loop"hole`\, n.
   1. (Mil.) A small opening, as in the walls of fortification,
      or in the bulkhead of a ship, through which small arms or
      other weapons may be discharged at an enemy.

   2. A hole or aperture that gives a passage, or the means of
      escape or evasion.

Source : WordNet®

loophole
     n 1: an ambiguity (especially one in the text of a law or
          contract) that makes it possible to evade a difficulty
          or obligation
     2: a small hole in a fortified wall; for observation or
        discharging weapons