early 15c., from Latin deducere "lead down, derive" (in Medieval Latin, "infer logically"), from de- "down" (see de-) + ducere "to lead" (see duke (n.)). Originally literal; sense of "draw a conclusion from something already known" is first recorded 1520s, from Medieval Latin. Related: Deduced; deducing.[deduce etymology, deduce origin, 英语词源]