c. 1200, literally "wind eye," from Old Norse vindauga, from vindr "wind" (see wind (n.1)) + auga "eye" (from PIE root *okw- "to see"). Replaced Old English eagþyrl, literally "eye-hole," and eagduru, literally "eye-door." Compare Old Frisian andern "window," literally "breath-door."

Originally an unglazed hole in a roof. Most Germanic languages later adopted a version of Latin fenestra to describe the glass version (such as German Fenster, Swedish fönster), and English used fenester as a parallel word till mid-16c.

Window dressing in reference to shop windows is recorded from 1853; figurative sense is by 1898. Window seat is attested from 1778. Window of opportunity (1979) is from earlier figurative use in U.S. space program, such as launch window (1963). Window-shopping is recorded from 1904.

Window shopping, according to the women, is the king of outdoor sports. Whenever a woman gets down town and has 2 or 3 hours and no money to spend, she goes window shopping. She gives the Poiret gowns and the thousand dollar furs the double O and then kids herself into believing she'd look like Lillian Russell or Beverly Bayne if she had 'em on. It's great for developing the imagination and one of the great secrets of conserving the bankroll. ... [Motor Age, Jan. 27, 1916]

mid-13c, "a portico or small room forming a projection, a room or building in the form of a large bay window;" mid-14c., "large recessed window, a bay window," from Old French oriol "hall, vestibule; oriel," and Medieval Latin oriolum "porch, small room, gallery," which are perhaps from Vulgar Latin *auraeolum, a dissimilation of aulaeolum, a diminutive of Latin aulaeum "curtain." "Although much research has been expended upon the history of this word, and especially upon the development of the current use in oriel window, the sense history remains in many points obscure and perplexed" [OED].

It projects from the outer face of the wall, being in plan actually hexagonal, semi-octagonal, or rectangular, etc., and is supported on brackets, corbels, or corbeling. When such a projecting feature rests upon the ground, or directly upon the foundation of the building, it is called a bay-window, or a bow-window. [Century Dictionary]

also dormer-window, "window standing vertically in a projection built out to receive it from a sloping roof," 1590s, from French dormeor "sleeping room," from dormir "to sleep," from Latin dormire (see dormant). So called because they were chiefly in upper bedrooms.