The Collaborative International Dictionary of English v.0.48:

Trench \Trench\, v. t. [imp. & p. p. Trenched; p. pr. & vb. n.
   Trenching.] [OF. trenchier to cut, F. trancher; akin to Pr.
   trencar, trenchar, Sp. trinchar, It. trinciare; of uncertain
   origin.]
   1. To cut; to form or shape by cutting; to make by incision,
      hewing, or the like.
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            The wide wound that the boar had trenched
            In his soft flank.                    --Shak.
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            This weak impress of love is as a figure
            Trenched in ice, which with an hour's heat
            Dissolves to water, and doth lose its form. --Shak.
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   2. (Fort.) To fortify by cutting a ditch, and raising a
      rampart or breastwork with the earth thrown out of the
      ditch; to intrench. --Pope.
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            No more shall trenching war channel her fields.
                                                  --Shak.
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   3. To cut furrows or ditches in; as, to trench land for the
      purpose of draining it.
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   4. To dig or cultivate very deeply, usually by digging
      parallel contiguous trenches in succession, filling each
      from the next; as, to trench a garden for certain crops.
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The Collaborative International Dictionary of English v.0.48:

Trench \Trench\, v. i.
   1. To encroach; to intrench.
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            Does it not seem as if for a creature to challenge
            to itself a boundless attribute, were to trench upon
            the prerogative of the divine nature? --I. Taylor.
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   2. To have direction; to aim or tend. [R.] --Bacon.
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   To trench at, to make trenches against; to approach by
      trenches, as a town in besieging it. [Obs.]
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            Like powerful armies, trenching at a town
            By slow and silent, but resistless, sap. --Young.
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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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WordNet (r) 3.0 (2006):

trench
    n 1: a ditch dug as a fortification having a parapet of the
         excavated earth
    2: a long steep-sided depression in the ocean floor [syn:
       trench, deep, oceanic abyss]
    3: any long ditch cut in the ground
    v 1: impinge or infringe upon; "This impinges on my rights as an
         individual"; "This matter entrenches on other domains"
         [syn: impinge, encroach, entrench, trench]
    2: fortify by surrounding with trenches; "He trenched his
       military camp"
    3: cut or carve deeply into; "letters trenched into the stone"
    4: set, plant, or bury in a trench; "trench the fallen
       soldiers"; "trench the vegetables"
    5: cut a trench in, as for drainage; "ditch the land to drain
       it"; "trench the fields" [syn: trench, ditch]
    6: dig a trench or trenches; "The National Guardsmen were sent
       out to trench"