forlorn (adj.) Look up forlorn at Dictionary.com
mid-12c., forloren "disgraced, depraved," past participle of obsolete forlesan "be deprived of, lose, abandon," from Old English forleosan "to lose, abandon, let go; destroy, ruin," from for- "completely" + leosan "to lose" (see lose). In the Mercian hymns, Latin perditionis is glossed by Old English forlorenisse.

Sense of "forsaken, abandoned" is 1530s; that of "wretched, miserable" first recorded 1580s. A common Germanic compound (cognates: Old Saxon farilosan, Old Frisian urliasa, Middle Dutch verliesen, Dutch verliezen, Old High German virliosan, German verlieren, Gothic fraliusan "to lose").

Commonly in forlorn hope (1570s), which is a partial translation of Dutch verloren hoop, in which hoop means "troop, band," literally "heap," and the sense of the whole phrase is of a suicide mission. The phrase is usually used incorrectly in English, and the misuse has colored the sense of forlorn. Related: Forlornly; forlornness.