Is it ensure, insure, or assure?
"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 misspelled eyrie (1660s) on the mistaken assumption that it derived from Middle English ey "egg."