Old English losian "be lost, perish," from los "destruction, loss," from Proto-Germanic *lausa- (cf. Old Norse los "the breaking up of an army;" Old English forleosan "to lose, destroy," Old Frisian forliasa, Old Saxon farliosan, Middle Dutch verliesen, Old High German firliosan, German verlieren), from PIE root *leu- "to loosen, divide, cut apart, untie, separate" (cf. Sanskrit lunati "cuts, cuts off," lavitram "sickle;" Greek lyein "to loosen, untie, slacken," lysus "a loosening;" Latin luere "to loose, release, atone for, expiate").
Replaced related leosan (a class II strong verb whose past participle loren survives in forlorn and lovelorn), from Proto-Germanic *leusanan (cf. Old High German virliosan, German verlieren, Old Frisian urliasa, Gothic fraliusan "to lose").
Transitive sense of "to part with accidentally" is from c.1200. Meaning "fail to maintain" is from mid-15c. Meaning "to be defeated" (in a game, etc.) is from 1530s. Meaning "to cause (someone) to lose his way" is from 1640s. To lose (one's) mind "become insane" is attested from c.1500. To lose out "fail" is 1858, American English. Related: Lost; losing.