From Old French 'trenche' (a cut), from 'trenchier' (to cut)—a trench is a 'cutting' in the earth.
A long, narrow excavation in the ground, used for military defense, drainage, or laying pipes.
From Old French 'trenche' (a cut, a gash, a ditch), from 'trenchier' (to cut), from Latin *trincare (to cut), possibly from 'truncare' (to cut off, to maim). A trench is etymologically a 'cutting' in the earth. Key roots: truncare (Latin: "to cut off, to maim, to shorten").