The Collaborative International Dictionary of English v.0.48:

Trench \Trench\, n. [OE. trenche, F. tranch['e]e. See Trench,
   v. t.]
   1. A long, narrow cut in the earth; a ditch; as, a trench for
      draining land. --Mortimer.
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   2. An alley; a narrow path or walk cut through woods,
      shrubbery, or the like. [Obs.]
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            In a trench, forth in the park, goeth she.
                                                  --Chaucer.
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   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.
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   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.
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