'arrear' originates from Old French/Anglo-French, specifically the word 'arrière' (meaning 'behind'), ultimately from Latin components such as 'ad' + 'retro' (toward the back).

'arrear' changed from Middle English forms (influenced by Anglo-French 'arere'/'arrière') and eventually became modern English 'arrear' (with the frequent plural form 'arrears').

Initially it meant 'at or toward the back/behind', but over time it evolved into the financial sense 'money owed that is behind schedule' (i.e., 'overdue payment').