boyaun.

1691 A. Swall tr. S. Le P. de Vauban New Method Fortification i. iv. 8 Boyau, is a Moat border'd with a Paraper [sic], which is drawn from one Trench to another for better Communication.

1757 Jrnl. 9 Aug. in N. J. O'Conor Servant of Crown (1938) 74 The Ennemy fired very slowly, and run another Boyeau behind the Garden near 300 Yards from the Fort.

1853 J. H. Stocqueler Mil. Encycl. 41/2 Boyau, a branch of a trench; a zigzag; a trench in rear of a battery, forming a communication with the magazine; a small gallery of a mine.

1862 F. A. Griffiths Artillerist's Man. (ed. 9) 263 Zig-zags, or Boyeaux of communication, are trenches made for the approaches from the parallels to the besieged place.

1918 Stars & Stripes 1 Mar. 2/2 The boyau deepened and we felt our way along the duck boards in single file. Yes, it was muddy!

1953 Huntington Libr. Q. 16 375 Canadian workmen feverishly dug and enlarged the boyaux, or trenches.

1989 B. I. Gudmundsson Stormtroop Tactics (1995) ii. 32 An early solution to the problem of crossing fire-swept terrain was the use of boyaux, shallow ditches running across no man's land, that, because they had originally been dug as communications trenches, were roughly perpendicular to the fighting trenches.