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
1. To cut; to form or shape by cutting; to make by incision,
hewing, or the like.
The wide wound that the boar had trenched
In his soft flank. --Shak.
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.
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.
No more shall trenching war channel her fields.
3. To cut furrows or ditches in; as, to trench land for the
purpose of draining it.
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.