A nightshirt is a garment intended for wear while sleeping. It is longer than most regular shirts, reaching down to the thighs or below the knees, leaving some of the legs uncovered. It is generally loose-fitting to avoid restricting the wearer's movement while sleeping.
Until the 16th century men slept naked or in a day-shirt; subsequently a night-shirt, varying in quality, was worn in bed. Nobles in the 16th century wore embroidered shirts or "wrought night-shirts". By the 19th century the night-shirt resembled a day-shirt with a loose, turned-down collar, or a loose, ankle-length nightgown was worn.
Occasionally worn in the 20th and 21st centuries by women as well.