Definitions
1.NounA slit in a castle wall; today, any similar window for shooting a ranged weapon or letting in light.
2.NounA method of escape, especially an ambiguity or exception in a rule or law that can be exploited in order to avoid its effect.
3.VerbTo prepare a building for defense by preparing slits or holes through which to fire on attackers
4.VerbTo exploit (a law, etc.) by means of loopholes.