Boyau definitions

Webster's 1828 Dictionary

BOY'AU, n. boy'o. In fortification, a ditch covered with a parapet, serving as a communication between two trenches.
BOY'-BLIND, a. Blind as a boy; undiscerning.

Webster's 1913 Dictionary

Boyau Boy"au, n.; pl. Boyaux or Boyaus. [F. boyau gut, a long and narrow place, and (of trenches) a branch. See Bowel.] (Fort.) A winding or zigzag trench forming a path or communication from one siegework to another, to a magazine, etc.