Webster's Revised Unabridged Dictionary · 1913

Bivouac

Bivouac ({not transcribed}) , noun

[French bivouac, bivac, prab. from German beiwache, or beiwacht; bei by, near + wachen to watch, wache watch, guard. See By, and Watch.]

(a)
(Military) The watch of a whole army by night, when in danger of surprise or attack.
(b)
(Military) An encampment for the night without tents or covering.

Bivouac , intransitive verb

(a)
(Military) To watch at night or be on guard, as a whole army.
(b)
(Military) To encamp for the night without tents or covering.