The Collaborative International Dictionary
Boyaus
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.
Wiktionary
boyaus
n. (plural of boyau English)