means A long, narrow ditch cut into the ground, whether for drainage, construction, or sheltering soldiers in war.

from From Old French 'trenche,' meaning a slice or cut, from the verb 'trenchier' — to cut or slice — which gives us 'trench' as something carved into the earth, and is the same family that left us 'trenchant' (sharply cutting words) and the 'trencher,' the cutting-board-plate of the medieval table. The deeper root is likely Latin 'truncare,' to lop or maim, a cousin of 'truncate.' So a trench is, at heart, simply a cut in the ground — though the World War I battlefields gave that humble cut its grim afterlife.