trou-de-loup
Trou"-de-loup", n.; pl. Trous-de-loup(Etym: [F. trou hole + de of + loup wolf.] (Mil.) Defn: 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.