early 13c., literally "wind eye," from Old Norse vindauga, from vindr "wind" (see wind (n.1)) + auga "eye. (see eye (n.)). Replaced Old English eagþyrl, literally "eye-hole," and eagduru, literally "eye-door."
Originally an unglazed hole in a roof, most Germanic languages adopted a version of Latin fenestra to describe the glass version, and English used fenester as a parallel word till mid-16c. Window dressing is first recorded 1790; figurative sense is from 1898. Window seat is attested from 1778. Window-shopping is recorded from 1922. Window of opportunity (1979) is from earlier figurative use in U.S. space program, e.g. launch window (1965).