Trou-de-loup

In mediaeval fortification, a trou de loup (French for "wolf hole"; plural trous de loup, also commonly referred to as a tiger pit in the East) was a type of booby trap or defensive obstacle. Each trou de loup consisted of an inverted conical pit about 2 m (6 feet) deep and 1.2 to 2 m (4 to 6 ft) wide at the top. At the bottom of the pit, a sharpened wooden stake would be hammered in. In some cases, the pit was concealed by light cover of wicker and a layer of soil.
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Noun
1. a sloping pit with a stake in the middle used as an obstacle to the enemy
(hypernym) pit, quarry, stone pit

(n.)
A pit in the form of an inverted cone or pyramid, constructed as an obstacle to the approach of an enemy, and having a pointed stake in the middle. The pits are called also trapholes.
  

Fr. ‘wolf traps’. Defensive potholes dug in front of Flemish lines at the Battle of Courtai to break up the French cavalry charge. 

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