[1] : The Collaborative International Dictionary of English v.0.48

abatis \ab"atis\, abattis \aba"ttis\, a^b".ati^s;
   french .a`b.a`t=e" n. f. abatis, abattis, mass of
   things beaten or cut down, fr. abattre. see abate. fort.
   a means of defense formed by felled trees, the ends of whose
   branches are sharpened and directed outwards, or against the
   enemy.
   1913 webster
see also:
abate 

[2] : WordNet (r) 2.0

abattis
     n : line of defense consisting of a barrier of felled or live
         trees with branches sharpened or with barbed wire
         entwined toward the enemy syn: abatis
see also:
abatis 

Abattis >> A Words
Abattis, definition of term: Abattis
abattis_pag1.html