trenchyoudaoicibaDictYouDict[trench 词源字典]
trench: [14] A trench is etymologically something ‘cut’ or ‘sliced’. The word was borrowed from Old French trenche ‘slice, cutting, ditch’, a derivative of trenchier ‘cut’ (from which English gets trenchant [14]). And this in turn went back to Latin truncāre ‘cut, mutilate’ (source of English truncate [15]), a derivative of truncus ‘tree-trunk, torso’ (source of English trunk) – the semantic link being the ‘cutting’ of branches from a tree or of limbs from a body.

The sense ‘ditch’ for trench comes of course from the notion of ‘cutting’ a long narrow hole in the ground (a similar inspiration underlies cutting ‘excavation for a railway, road, etc’). Trencher ‘platter’ [14] came from the Anglo-Norman derivative trenchour, and originally denoted both a board for ‘cutting’ food up on and a ‘slice’ of bread used as a plate.
=> trenchant, trencher, truncate, trunk[trench etymology, trench origin, 英语词源]
trench (n.)youdaoicibaDictYouDict
late 14c., "track cut through a wood," later "long, narrow ditch" (late 15c.), from Old French trenche "a slice, cut, gash, slash; defensive ditch" (13c., Modern French tranche), from trenchier "to cut, carve, slice," possibly from Vulgar Latin *trincare, from Latin truncare "to cut or lop off" (see truncate). Trenches for military protection are first so called c. 1500. Trench warfare first attested 1918. Trench-coat first recorded 1916, a type of coat worn by British officers in the trenches during World War I.