ab·a·tis 
(ăbə-tē′, -tĭs)
(ăbə-tē′, -tĭs)n. pl. ab·a·tis (-tēz′) or ab·a·tis·es (-tĭ-sĭz)
A defensive obstacle made by laying felled trees on top of each other with branches, sometimes sharpened, facing the enemy.
[French, pile of things thrown down, from Old French abateis; akin to abattre, to throw down; see ABATE.]