Noun
(historical) A slit or hole above the entrance to a fortification, thought to provide access for defenders to kill invaders.
(historical, rare) A chamber above the entrance to a fortification where defenders hide and shoot at invaders trapped in the entryway below.
Murder Hole
A waterhole or pit in a bog where the bodies of murder victims were thrown.
Alternative form of murder hole
A deep pit used for drowning malefactors as a punishment.
Source: en.wiktionary.orgmurder-hole