Old English losian "be lost, perish," from los "destruction, loss," from Proto-Germanic *lausa- (source also of 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, as well as English -less, loss, loose). The Germanic word is from PIE *leus-, an extended form of root *leu- "to loosen, divide, cut apart."
The verb also is merged with, or has taken the (weaker) sense of, the related Middle English leese "be deprived of, lose" (Old English leosan, a class II strong verb whose past participle loren survives in forlorn and love-lorn), from Proto-Germanic *leusanan (source also of Old High German virliosan, German verlieren, Old Frisian urliasa, Gothic fraliusan "to lose").
Hence lose in the transitive senses "part with accidentally, be deprived of, miss the possession or knowledge of" (money, blood, sleep, hair, etc.), c. 1200; "fail to keep, lose track of" (mid-13c.). Meaning "fail to preserve or maintain" is from mid-15c. Meaning "fail to gain or win" (something) is from c.1300; intransitive meaning "fail to win" (a game, contest, lawsuit, etc.) is from late 14c. Meaning "to cause (someone) to lose his way" is from 1640s; meaning "cease to have, be rid of" (something unwanted) is from 1660s.
To lose heart "become discouraged" is from 1744; to lose (one's) heart "fall in love" is from 1630s. To lose (one's) mind "become insane" is attested from c. 1500. To lose out "fail" is 1858, American English. To lose it "become distraught, break down and lose control of oneself" is by 1990s; the it probably being one's self-control or grip on reality. Related: Lost; losing.
c. 1300; "wasted, ruined, spent in vain," c. 1500; also "no longer to be found, gone astray" (1520s), past-participle adjectives from lose. Meaning "spiritually ruined, inaccessible to good influence" is from 1640s. Related: Lostness.
Of battles, games, etc. in which one has been defeated, 1724; hence Lost Cause in reference to the bid for independence by the southern states of the U.S., first as the title of the 1866 pro-Southern history of the CSA and the rebellion written by Virginia journalist E.A. Pollard (1832-1872). Lost Generation in reference to the youth that came of age when World War I broke is first attested 1926 in Hemingway's "The Sun Also Rises," where he credits it to Gertrude Stein. Lost-and-found as the name of a department where misplaced articles are brought or sought is by 1907.
It forms all or part of: absolute; absolution; absolve; analysis; analytic; catalysis; catalyst; catalytic; dialysis; dissolve; electrolysis; electrolyte; forlorn; Hippolytus; hydrolysis; -less; loess; loose; lorn; lose; loss; Lysander; lysergic; lysis; -lysis; lyso-; lysol; lytic; -lytic; palsy; paralysis; pyrolusite; resolute; resolution; resolve; soluble; solute; solution; solve; solvent.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit lunati "cuts, cuts off," lavitram "sickle;" Greek lyein "to loosen, untie, slacken," lysus "a loosening;" Latin luere "to loose, release, atone for, expiate;" Old Norse lauss "loose, free, unencumbered; vacant; dissolute;" Old English losian "be lost, perish."
"to lose hope, be without hope," mid-14c., despeiren, from Old French despeir-, stressed stem of desperer "be dismayed, lose hope, despair," from Latin desperare "to despair, to lose all hope," from de "without" (see de-) + sperare "to hope," from spes "hope" (from PIE root *spes- "prosperity;" see speed (n.)). Related: Despaired; despairing; despairingly.
Old English forgietan "lose the power of recalling to the mind; fail to remember; neglect inadvertently," from for-, used here probably with privative force, "away, amiss, opposite" + gietan "to grasp" (see get (v.)). To "un-get," hence "to lose" from the mind. A common Germanic construction (compare Old Saxon fargetan, Old Frisian forjeta, Dutch vergeten, Old High German firgezzan, German vergessen "to forget"). The physical sense would be "to lose (one's) grip on," but that is not recorded in any historical Germanic language. Figurative sense of "lose care for" is from late 13c. Related: Forgetting; forgot; forgotten.
"lose the ability to maintain compensation," 1912, probably a back-formation from decompensation. Related: Decompensated; decompensating.
Old English colian, "to lose warmth," also figuratively, "to lose ardor;" cognate with Old Saxon kolon, Dutch koelen, Old High German chuolan, German kühlen, all from the root of cool (adj.). Transitive meaning "to cause to lose warmth, reduce the temperature of" is from late 14c. Related: Cooled; cooling.
Figurative meaning "abate the intensity of" is from c. 1300. To cool (one's) heels" wait in attendance, "generally applied to detention at a great man's door" [Century Dictionary] is attested from 1630s; probably the notion is "to rest one's feet after walking."