abatis
noun
ab·a·tis ˈa-bə-ˌtē 
ˈa-bə-təs
ˈa-bə-təs plural abatis ˈa-bə-ˌtēz or abatises ˈa-bə-tə-səz
or abatises ˈa-bə-tə-səz : a defensive obstacle formed by felled trees with sharpened branches facing the enemy
Word History
Etymology
borrowed from French, literally, "act of felling, things felled," going back to Old French abateiz, from abatre "to strike down, fell" + -eiz, -eis, resultative suffix, going back to Vulgar Latin *-ātīcium, neuter of *-ātīcius, from Latin -ātus -ate entry 3 + -īcius, adjective suffix — more at abate
First Known Use
1757, in the meaning defined above