Fortification . a long, narrow excavation in the ground, the earth from which is thrown up in front to serve as a shelter from enemy fire or attack.

trenches, a system of such excavations, with their embankments, etc.

a deep furrow, ditch, or cut.

Oceanography . a long, steep-sided, narrow depression in the ocean floor.

to surround or fortify with trenches; entrench.

to cut a trench in.

to set or place in a trench.

to form (a furrow, ditch, etc.) by cutting into or through something.

to make a cut in; cut into; carve.

to dig a trench. ?

trench on or upon,

to encroach or infringe on.

to come close to; verge on

His remarks were trenching on poor taste.

noun

arroyo , canal , cut , depression , dike , drain , drill , dugout , earthwork , entrenchment , excavation , fosse , foxhole , furrow , gorge , gulch , gully , gutter , hollow , main , moat , pit , rut , sink , trough , tube , waterway , bank , banquette , canyon , carve , channel , chase , ditch , encroach , gash , groove , parados , slash , slice