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1620s, "abatement," alteration of 16c. French descompte, from Medieval Latin discomputus (source of Italian disconto), from discomputare (see discount (v.)). Meaning "deduction for early payment" is from 1680s; meaning "reduction in the price of goods" attested by 1837.
1620s, "reckon as an abatement or deduction," from Old French desconter (13c., Modern French décompter), from Medieval Latin discomputare, from dis- (see dis-) + computare "to count" (see count (v.)). Hence, "to abate, deduct" (1650s), and figurative sense "to leave out of account, disregard" (1702). Related: Discounted; discounting.