'deductor' originates from Latin, specifically the word 'dēductus' (from 'dēdūcere'), where the root 'dē-' meant 'down, away' and 'dūcere' meant 'to lead'; in English it combines with the agentive suffix '-or' meaning 'one who performs an action'.

'deductus' transformed into the English verb 'deduct' via Late Latin and French influence, and the English agent noun 'deductor' was later formed by adding '-or' to 'deduct'.

Initially, it related to 'leading down or away' and then to 'subtracting or taking away,' which developed into the modern sense of 'one who subtracts or withholds an amount'.