glacis

noun5

1. •
   A gentle incline.

   • The foam of these great ruins mounts in an instant to the ridge of the sand glacis, swiftly fleets back again, and is met and buried by the next breaker. — 1880
2. •
   A gentle sloping landform created by the deposition or erosion of material.
3. •
   A gentle incline in front of a fortification which protects it from cannon fire and exposes attackers to more effective return fire from defenders.

   • [T]ook his place with solemn Air 'midst the rest, who kept their valiant faces And levelled weapons still against the glacis. — 1823
4. •
   In full glacis plate: the angled armour plate on the front of a tank which protects it from projectiles; also (often nautical), such a plate protecting an opening (for example, on a ship).
5. •
   A device for sorting mail which slides parcels across a sloped surface.