1902, "model to display clothes," from French mannequin (15c.), from Dutch manneken "model of the human figure used by artists," literally "little man" (see manikin). A French form of the same word that yielded manikin, and sometimes mannequin was used in English in a sense "artificial man" (especially in translations of Hugo). Originally of persons, in a sense where we might use "model." Later (by 1931) of artificial human model figures to display clothing.
A mannequin is a good-looking, admirably formed young lady, whose mission is to dress herself in her employer's latest "creations," and to impart to them the grace which only perfect forms can give. Her grammar may be bad, and her temper worse, but she must have the chic the Parisienne possesses, no matter whether she hails from the aristocratic Faubourg St. Germain or from the Faubourg Montmartre. ["The Bystander," Aug. 15, 1906]