impotent (adj.) Look up impotent at Dictionary.com
late 14c., "physically weak, enfeebled, crippled," from Old French impotent "powerless, weak, incapable of doing," from Latin imponentem (nominative impotens) "lacking control, powerless, feeble; lacking self-control," from assimilated form of in- "not, opposite of" (see in- (1)) + ponentem (nominative potens) "potent" (see potent).

Meaning "having no power to accomplish anything" is from mid-15c.; that of "completely lacking in sexual power" (of males) is from mid-15c. Middle English also had a native term for this: Cunt-beaten (mid-15c.). The figurative sense in Latin was "without self-control, headstrong, violent, ungovernable, lacking self-restraint," which sometimes is found in English (OED cites examples from Spenser, Massinger, Dryden, and Pope). Related: Impotently.