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.
      [1913 Webster]

            The wide wound that the boar had trenched
            In his soft flank.                    --Shak.
      [1913 Webster]

            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.
      [1913 Webster]

   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.
      [1913 Webster]

            No more shall trenching war channel her fields.
                                                  --Shak.
      [1913 Webster]

   3. To cut furrows or ditches in; as, to trench land for the
      purpose of draining it.
      [1913 Webster]

   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.
      [1913 Webster]