Borrowed from French bivouac (earlier biouac, bivac), from Alemannic German Biiwacht (reinforcements of guard or town watch), from bii- + Wacht (watch, guard).

bivouac (third-person singular simple present bivouacs or bivouacks, present participle bivouacing or bivouacking, simple past and past participle bivouacked)

From earlier bivoie, biouac, bivac, from Alemannic German Biiwacht (), from bii- (by-) + Wacht (watch, guard).

a patrol of citizens added - in time of alarm or commotion - to the regular town watch