Synonyms:
* Powerless: Lacking power or strength
* Weak: Lacking physical or mental strength
* Ineffective: Not producing the desired effect
* Futile: Pointless or useless
* Helpless: Unable to act or defend oneself
* Sterile: Unable to reproduce
Antonyms:
* Powerful: Having great strength or influence
* Strong: Physically or mentally robust
* Effective: Producing the desired result
* Potent: Having great power or influence
* Capable: Able to do something
* Fertile: Able to reproduce
It's important to note that the best synonym or antonym for "impotent" depends on the specific context in which it is used. For example, "powerless" might be a better synonym than "sterile" when referring to a government that is unable to enact change.