1856, "capable of being withdrawn," especially from one's taxes or income, with -ible + Latin deducere "lead down, derive" (in Medieval Latin, "infer logically"), from de "down" (see de-) + ducere "to lead," from PIE root *deuk- "to lead." As a noun, "amount of a loss which must be borne by the policy-holder in an insurance claim," by 1927. The older adjective is deducible (1610s).
