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bivouac: bivouac: [18] Bivouac appears to be of Swiss- German origin. The early 19th-century writer Stalder noted that the term beiwacht (bei ‘additional’ + wacht ‘guard’ – a relative of English watch and wake) was used in Aargau and Zürich for a sort of band of vigilantes who assisted the regular town guard. Beiwacht was borrowed into French as bivac, and came to English in a later form bivouac.

Its original application in English was to an army remaining on the alert during the night, to guard against surprise attack; in so doing, of course, the soldiers did not go to sleep in their tents, and from this the term bivouac spread to ‘improvised, temporary camp’, without the luxury of regular tents.
=> wake, watch
bunk (v.): "to sleep in a bunk," 1840, originally nautical, from bunk (n.1). Related: Bunked; bunking.
hay (n.): "grass mown," Old English heg (Anglian), hieg, hig (West Saxon) "grass cut or mown for fodder," from Proto-Germanic *haujam (cognates: Old Norse hey, Old Frisian ha, Middle Dutch hoy, German Heu, Gothic hawi "hay"), literally "that which is cut," or "that which can be mowed," from PIE *kau- "to hew, strike" (cognates: Old English heawan "to cut;" see hew). Slang phrase hit the hay (pre-1880) was originally "to sleep in a barn;" hay in the general figurative sense of "bedding" is from 1903; roll in the hay (n.) is from 1945.
sandman (n.): bringer of sleep in nursery lore, 1861, from sand (n.) in reference to hard grains found in the eyelashes on waking; first attested in a translation from the Norwegian of Andersen (his Ole Lukoie "Ole Shut-eye," about a being who makes children sleepy, came out 1842), and perhaps partly from German Sandmann. More common in U.S.; dustman with the same sense is attested from 1821.
Somnus (n.): "sleep personified; the god of sleep in Roman mythology," equivalent of Greek Hypnos, son of Night and brother of Death, 1590s, from Latin somnus "sleep, drowsiness," from PIE *swep-no-, from root *swep- (1) "to sleep" (cognates: Sanskrit svapnah, Avestan kvafna-, Greek hypnos, Lithuanian sapnas, Old Church Slavonic sunu, Old Irish suan, Welsh hun "sleep," Latin sopor "a deep sleep," Old English swefn, Old Norse svefn "a dream").
truckle (v.): "give up or submit tamely," 1610s, originally "sleep in a truckle bed" (see truckle (n.)). Meaning "give precedence, assume a submissive position" (1650s, implied in truckling) is perhaps in reference to that type of bed being used by servants and inferiors or simply occupying the lower position. Related: Truckled; truckling.