Is it ensure, insure, or assure?
late Old English scirgerefa "representative of royal authority in a shire," from scir (see shire) + gerefa "chief, official, reeve" (see reeve). As an American county official, attested from 1660s; sheriff's sale first recorded 1798. Sheriff's tooth (late 14c.) was a common name for the annual tax levied to pay for the sheriff's victuals during court sessions.