impotent (adj.) Look up impotent at Dictionary.com
late 14c., "physically weak, enfeebled, crippled," from Old French impotent "powerless, weak, incapable," from Latin imponentem (nominative impotens) "lacking control, powerless," 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." Related: Impotently.