"inlet, recess in the shore of a sea or lake," c. 1400, from Old French baie, Late Latin baia (source of Spanish and Portuguese bahia, Italian baja), which is perhaps ultimately from Iberian (Celtic) bahia.
"opening in a wall," especially a space between two columns, late 14c. from Old French baee "opening, hole, gulf," noun use of fem. past participle of bayer "to gape, yawn," from Medieval Latin batare "gape," perhaps of imitative origin. Meaning "compartment for storage: is from 1550s. Somewhat confused with bay (n.1) "inlet of the sea," it is the bay in sick-bay and bay window (early 15c.).
"deep-toned howl of a dog," early 14c., earlier "howling chorus raised (by hounds) when in contact with the hunted animal," c. 1300, from Old French bayer, from PIE root *bai- echoic of howling (compare Greek bauzein, Latin baubari "to bark," English bow-wow; also see bawl).
From the condition of a hunted animal comes the transferred sense of "final encounter," and thence, on the notion of turning to face the danger when further flight or escape is impossible, at bay.
"reddish-brown," usually of horses, mid-14c., from Anglo-French bai (13c.), Old French bai, from Latin badius "chestnut-brown" (used only of horses), from PIE root *badyo- "yellow, brown" (source also of Old Irish buide "yellow"). As a noun, elliptical for a horse of this color.
laurel shrub (Laurus nobilis, source of the bay-leaf), late 14c., but meaning originally only the berry, from Old French baie (12c.) "berry, seed," from Latin baca, bacca "berry, fruit of a tree or shrub, nut" (source also of Spanish baya, Old Spanish bacca, Italian bacca "a berry"), a word of uncertain origin. De Vaan writes that connection with Greek Bakhos "Bacchus" is difficult, as the Greek word probably was borrowed from an Asian language. Some linguists compare Berber *bqa "blackberry, mulberry," and suggest a common borrowing from a lost Mediterranean language.
Extension of the word to the shrub itself is from 1520s. The leaves or sprigs were woven as wreaths for conquerors or poets, hence "honorary crown or garland bestowed as a prize for victory or excellence" (1560s). Bay-leaf is from 1630s. Bay-berry (1570s) was coined after the sense of the original word had shifted to the tree.