Any of various close-fitting garments; specifically (a) a knee-length, tight-fitting style of coat worn by men in the second half of the 17th cent. and the early 18th cent.; (b) a tight-fitting style of coat worn by women for riding in the second half of the 17th cent. and in the early 18th cent.; (c) any tight-fitting garment of the second half of the 17th cent. as understood in later usage to be a coat or waistcoat.
Mid 17th century; earliest use found in Thomas Blount (1618–1679), antiquary and lexicographer. From French justaucorps, denoting any of various close-fitting garments for men and women from juste close-fitting + au to the + corps body.