bivouac (n.) Look up bivouac at Dictionary.com
1702, "encampment of soldiers that stays up on night watch in the open air, dressed and armed," from French bivouac (17c.), said to be a word from the Thirty Years' War, ultimately from Swiss/Alsatian biwacht "night guard," from bei- (from Old High German bi- "by," here perhaps as an intensive prefix; see by) + wacht "guard" (from Proto-Germanic *wahtwo, from PIE root *weg- "to be strong, be lively"). Sense of "outdoor camp" is from 1853. According to OED not a common word in English before the Napoleonic Wars. Italian bivacco is from French. As a verb, 1809, "to post troops in the night;" meaning "camp out-of-doors without tents" is from 1814.