knickers (n.)

1866, in reference to loose-fitting pants for men worn buckled or buttoned at the waist and knees, shortening of knickerbockers (1859), said to be so called for their resemblance to the trousers of old-time Dutchmen in Cruikshank's illustrations for Washington Irving's "History of New York" (see Knickerbocker). As "short, loose-fitting undergarment for women," by 1882, now the usual sense.