Discarded, tossed out. This term is often used in the phrase go out the window, as in For the town planners past experience seems to have gone out the window. It alludes to unwanted items being hurled out of the window. [First half of 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.