"a metropolis; a very large, heavily populated urban complex," 1832, from Greek megas (genitive megalou) "great" (see mickle) + polis "city" (see polis). The word was used in classical times as an epithet of great cities (Athens, Syracuse, Alexandria), and it also was the name of a former city in Arcadia. Related: Megalopolitan.
"eagle's nest," 1580s (attested in Anglo-Latin from early 13c.), from Old French aire "nest," Medieval Latin area "nest of a bird of prey" (12c.), perhaps from Latin area "level ground, garden bed" [Littré], though some doubt this [Klein]. Another theory connects it to atrium. Formerly spelled eyrie (1660s) on the mistaken assumption that it derived from Middle English ey "egg."
1560s in medical use, "ring-like area or space," from a Medieval Latin misspelling of Latin anulus "little ring, finger ring," a diminutive of anus "ring" (see anus).