The Collaborative International Dictionary of English v.0.48:
Trench \Trench\, n. [OE. trenche, F. tranch['e]e. See Trench,
1. A long, narrow cut in the earth; a ditch; as, a trench for
draining land. --Mortimer.
2. An alley; a narrow path or walk cut through woods,
shrubbery, or the like. [Obs.]
In a trench, forth in the park, goeth she.
3. (Fort.) An excavation made during a siege, for the purpose
of covering the troops as they advance toward the besieged
place. The term includes the parallels and the approaches.
To open the trenches (Mil.), to begin to dig or to form the
lines of approach.
Trench cavalier (Fort.), an elevation constructed (by a
besieger) of gabions, fascines, earth, and the like, about
half way up the glacis, in order to discover and enfilade
the covered way.
Trench plow, or Trench plough, a kind of plow for opening
land to a greater depth than that of common furrows.