c.1370,
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 Fr. 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.
[ahyl] 
