"opening in a wall," early 14c. (especially bay window, c.1400), from O.Fr. baee "opening, hole, gulf," noun use of fem. pp. of bayer "to gape, yawn," from M.L. batare "gape," perhaps of imitative origin. Sick-bay "forepart of a ship's main deck used as a hospital" is from 1580s, from the notion of a
"howl of a hound" (especially when hunting), c.1300, from O.Fr. bayer, from PIE base *bai- echoic of howling (cf. Gk. bauzein, L. baubari "to bark," Eng. bow-wow; cf. also bawl). Noun meaning "cornering of a hunted animal" is also 14c. At bay (1640s) is from special sense of "chorus raised by hounds
in conflict with quarry," and reflects the former more widespread use of at
"reddish-brown," mid-14c., from Anglo-Fr. bai, from O.Fr. bai, from L. badius "chestnut-brown" (used only of horses), from PIE *badyo- "yellow, brown" (cf. O.Ir. buide "yellow"). Also elliptical for a horse of this color.
"shrub" (Laurus nobilis, source of the bay leaf), late 14c., originally only of the berry, from O.Fr. baie (12c.) "berry, seed," from L. baca "berry." Extension to the shrub itself is from 1520s. The leaves or sprigs were woven as wreaths for conquerors or poets. Bayberry first recorded 1570s.