1756, "a kind of loose gown worn by women," from French négligée, noun use of fem. past participle of négligier "to neglect" (14c.), from Latin neglegere "to disregard, not heed, not trouble oneself about," also "to make light of" (see neglect (v.)).
So called in comparison to the elaborate costume of a fully dressed woman of the period. Grose ["Dictionary of the Vulgar Tongue," 1788] reports it "vulgarly termed a neggledigee." Borrowed again, 1835; the modern sense "semi-transparent, flimsy, lacy dressing gown" is yet another revival, first recorded 1930. It also was used in the U.S. funeral industry mid-20c. for "shroud of a corpse."