Camped temporarily in the open air, especially without tents or full equipment, as soldiers often do during military campaigns.
From French 'bivouac,' borrowed from German 'Beiwacht' (extra guard watch). English adopted this term during the Napoleonic Wars and it became standard military terminology.
During the American Civil War, soldiers wrote letters home describing 'bivouacking'—a deceptively gentle word for sleeping outdoors in winter with minimal shelter, which killed more soldiers than actual combat due to disease and exposure.
Complete word intelligence in one call. Free tier — 50 lookups/day.