Fr: night gown
Initially, as the name implies, a night or morning gown.Not the white, linen, possibly sheer kind, but the kind of wrapping gown that even a modern person would wear to greet the post man. During the late 17th century, when the procedure of royal rising was a public (insofar as the presence of selected nobles could be called publicity) event, négligé was worn at home between rising and seriously starting a days' work, also in the presence of visitors.
Over the course of time, négligée (usually the robe à la française) was worn in the streets as well, became everyday dress, and finally served as court or wedding dress. The meaning of the word "négligée" also changed from denotig a morning/house gown to anything that wasn't formal court wear. See deshabillé.