late 14c., ele, from O.Fr. ele "wing" (of a church), from L. ala, related to axilla "wing, upper arm, armpit," from PIE *aks- "axis" (see axis
), via a suffixed form *aks-la-. The root meaning in "turning" connects it with axle and axis. Confused 15c. with unrelated ile "island"
(perhaps from notion of a "detached" part of a church), and so it took an -s- when isle did, c.1700; by 1750 it had acquired an a-, on the model of French cognate aile. The word also was confused with alley, which gave it the sense of "passage between rows of pews or seats" (1731), which was then extended to railway cars, theaters, etc.