'arrearage' originates from the noun 'arrear' + the noun-forming suffix '-age' (from Old French '-age'), used in English to indicate a state or condition; 'arrear' itself is used for being 'behind' or an amount due.

'arrear' entered English from Old French 'arere' / 'arriere' (meaning 'behind'); Middle English used 'arreer'/'arrear' for 'that which is behind or overdue', and English later formed 'arrearage' (arranged as 'arrear' + '-age') to denote the state or the sum overdue.

Initially it referred generally to the condition of being 'behind' (in a spatial or chronological sense), and over time it specialized to mean the condition of being behind in payments and the sums owed (overdue payments).