1. (formerly) a mound of earth inside a fort from which heavy gun can be fired over the parapet;
The Collaborative International Dictionary of English v.0.48:
Barbette \Bar*bette"\, n. [F. Cf. Barbet.] (Fort.)
A mound of earth or a platform in a fortification, on which
guns are mounted to fire over the parapet.
En barbette, In barbette, said of guns when they are
elevated so as to fire over the top of a parapet, and not
Barbette gun, or Barbette battery, a single gun, or a
number of guns, mounted in barbette, or partially
protected by a parapet or turret.
Barbette carriage, a gun carriage which elevates guns
sufficiently to be in barbette. [See Illust. of
[1913 Webster] Barbican
WordNet (r) 3.0 (2006):
n 1: (formerly) a mound of earth inside a fort from which heavy
gun can be fired over the parapet