cunette
A trench dug in a moat to allow for drainage, or as an extra obstacle for attackers.
Ford's Ravelin.—Completed in its ditch, ſluices, cunette, aqueducts, ſcarp, and counterſcarp walls; […]
Where it comes from
From French cunette (possibly also lacunette), from Italian cunetta (“cunette”), said to be from lacunetta, diminutive of lacuna (“ditch; lagoon; gap”), from Latin lacūna (“hole, pit; cavity, cleft, hollow, opening; gap, void”), from lacus (“lake”), from Proto-Indo-European *lókus (“lake, pool”).
Adapted from the Wiktionary entry cunette (CC BY-SA 4.0).