shift (n.2)youdaoicibaDictYouDict
"body garment, underclothing," 1590s, originally used alike of men's and women's pieces, probably from shift (n.1), which was commonly used in reference to a change of clothes. In 17c., it began to be used as a euphemism for smock, and was itself displaced, for similar reasons of delicacy, in 19c. by chemise.