Boy'au, n.

Boy'au (boy'o), n.; pl. BOY'AUX or BOY'AUS. [Fr. boyau, gut, a long and narrow place, and (of trenches) a branch. See BOWEL.] (Fort.) A small trench, or a branch of a trench, leading to a magazine, or to any particular point. They are generally called boyaus of communication. Scott's Mil. Dict.