Discount
early 17th century: from obsolete French descompte (noun), descompter (verb), or (in commercial contexts) from Italian ( di)scontare, both from medieval Latin discomputare, from Latin dis- (expressing reversal) + computare (see compute).
wiktionary
Alteration of French descompte, décompte, from Old French disconter, desconter(“reckon off, account back, discount”), from Medieval Latin discomputō(“I deduct, discount”), from Latin dis-(“away”) + computō(“I reckon, count”).
etymonline
discount (n.)
1620s, "abatement" (a sense now obsolete), alteration of French descompte (16c., Modern French décompte), from Medieval Latin discomputus (source of Italian disconto), from discomputare, from dis- (see dis-) + computare "to count" (see compute). Commercial meaning "deduction for early or prompt payment" is from 1680s; meaning "a reduction in the price of goods" attested by 1837.
discount (v.)
1620s, "reckon as an abatement or deduction" (a sense now obsolete), from Old French desconter "reckon off, account back" (13c., Modern French décompter), from Medieval Latin discomputare, from dis- "away, from" (see dis-) + computare "to reckon, to count" (see compute). Hence, "to abate, deduct" (1650s), and figurative sense "to leave out of account, disregard" (1702). Formerly also discompt. Commercial sense of "make a deduction from, put a reduced price upon" is by 1977. Related: Discounted; discounting.
