bivouac
Concise Oxford English Dictionary © 2008 Oxford University Press:
bivouac /ˈbɪvʊak, ˈbɪvwak/
▶noun a temporary camp without tents or cover. ▶verb (bivouacs, bivouacking, bivouacked) stay in a bivouac.
– origin C18: from Fr., prob. from Swiss Ger. Bîwacht ‘additional guard at night’.
'bivouac' also found in these Oxford entries:

