mid-14c., "passage in a house; open passage between buildings; walkway in a garden," from Old French alee (13c., Modern French allée) "a path, passage, way, corridor," also "a going," from fem. of ale, past participle of aler "to go," which ultimately may be a contraction of Latin ambulare "to walk," or from Gallo-Romance allari, a back-formation from Latin allatus "having been brought to" [Barnhart]. Cf. sense evolution of gate. Applied by c.1500 to "long narrow enclosure for playing at bowls, skittles, etc." Used in place names from c.1500.
The word is applied in American English to what in London is called a mews, and also is used there especially of a back-lane parallel to a main street (1729). To be up someone's alley "in someone's neighborhood" (literally or figuratively) is from 1931; alley-cat attested by 1890.