auditor n.

early 14c., "official who receives and examines accounts;" late 14c., "a hearer, one who listens," from Anglo-French auditour (Old French oieor "listener, court clerk," 13c.; Modern French auditeur), from Latin auditor "a hearer, a pupil, scholar, disciple," in Medieval Latin "a judge, examiner of accounts," from auditus, past participle of audire "to hear" (from PIE root *au- "to perceive"). The process of receiving and examining accounts formerly was done, and vouched for, orally. Related: Auditorial.