1640s, "derivative" (a sense now obsolete); from 1660s in logic, "consisting of deduction; based on inference from accepted principles," from Latin deductivus"derivative," from deduct-, past-participle stem of deducere "to lead down, derive" (in Medieval Latin, "infer logically"), from de "down" (see de-) + ducere "to lead," from PIE root *deuk- "to lead." Related: Deductively.
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