Etymology From Knickerbocker + -s, after the short breeches worn by Diedrich Knickerbocker in George Cruikshank's illustrations of Washington Irving's 1809 A History of New York.
1
Men's or boys' baggy knee breeches, of a type particularly popular in the early 20th century.
Five men and a woman, two young girls,[…], and a boy […] are at the machines sewing knickerbockers, “knee-pants” in the Ludlow Street dialect.1890, Jacob A[ugust] Riis, “The Sweaters of Jewtown”, in How the Other Half Lives: Studies among the Tenements of New York, New York, N.Y.: Charles Scribner’s Sons, →OCLC, page 125:
[…] and some gems that represent the tasseled garment that the leader wears show it in a distinctly religious connection. On a gem from Zakro it [the sistrum] is being being carried by a man who does not wear the loin-cloth, but a baggy kind of knickerbockers like the Moslem trousers of to-day.1907, Ronald M. Burrows, The Discoveries In Crete, page 37:
1 more example
And it was early morning, and the world was moist, when the crystal-gazer's husband, a freak in knickerbockers with an open coppish and a sabbath gamp, came over the stones outside his house to meet the holy travellers.a. 1954 (date written), Dylan Thomas, “The Holy Six”, in Adventures in the Skin Trade (A New Directions Paperbook; no. 183), New York, N.Y.: New Directions Publishing Corporation, published 1969, →ISBN, page 129: