A slope extending down from a fortification.(noun)
A neutral area separating conflicting forces.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "glacis" in a sentence
"The glacis is the smooth ground outside the ditch."
"Thus the ground beyond the ditch, that is, the glacis, covers the walls from the shot of a besieger, and renders it extremely difficult to reach them."
"The purpose of the glacis, which is an inclined plane, is to expose an attacking party to the fire of the guns, which are so placed as to sweep it from the crest of the counterscarp to the edge of the beach."