ab·a·tis (āb'ə-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.]