- deduction early 15c., "action of deducting," from M.Fr. déduction or directly from L. deductionem (nom. deductio), noun of action from pp. stem of deducere (see DEDUCE (Cf. deduce)). Meaning "that which is deducted" is from 1540s. As a term in logic, from L.L. use of deductio as a loan-translation of Gk. apagoge.
Etymology dictionary. 2014.