Knickers is a word used to refer to two very different items of clothing.

As an abbreviation for knickerbockers, knickers is a term for mens' or boys' baggy knee trousers, of a type particularly popular in the early 20th century. Golfers' plus twos and plus fours, now also generally a thing of the past, are trousers of this type. Before World War II, skiiers often wore knickerbockers too.

The term came from the fictional author of Washington Irving's History of New York, (published 1809), Diedrich Knickerbocker, an old-fashioned Dutch New Yorker in Irving's satire of chatty and officious local history. In fact, Washington Irving had a real friend named Herman Knickerbocker, whose name he borrowed. And the upstate Knickerbocker clan have all descended from a single immigrant ancestor, Harmen Jansen van Wye, who invented the name upon arriving in New Amsterdam and signed a document with a variant of it in 1682. After Irving's History, by 1831, "Knickerbocker" had become a local bye-word for quaint Dutch-descended New Yorkers, with their old-fashioned ways and their long-stemmed pipes and knee-breeches long after the fashion had turned to trousers. Thus the "New York Knickerbockers" were an amateur social and athletic club organized on Manhattan's (Lower) East Side in 1842, largely to play "base ball" according to written rules; on June 19, 1846 the New York Knickerbockers played the first game of "base ball" organized under those rules, in Hoboken, New Jersey, and were trounced 23 - 1.

Thus the locally-brewed "Knickerbocker Beer;" thus the gossip columnist "Cholly Knickerbocker;" thus the extremely high-toned Knickerbocker Club still in a neo-Georgian mansion on Fifth Avenue at 62nd Street, which was founded in 1871 when some members of the Union Club became concerned that admission policies weren't strict enough; and thus the New York Knicks who are covertly the "New York Knickerbockers."

In Britain, knickers is a term for panties or similar women's undergarments: "Don't get your knickers in a twist" (i.e. "Don't panic," or, in US usage "don't get your panties in a wad."). George Cruikshank, whose illustrations are classic icons for Charles Dickens' works, also did the illustrations for Irving's droll History of New York when it was published in London. He showed the old-time Knickerbockers in their loose Dutch breeches, and by 1859, short loose ladies undergarments, a kind of abbreviated version of pantaloons, were knickers in England. After World War I, very loose ladies' knickers were called "taxi treats", when the driver was asked to take the long way round the Park.