Underpower refers to the lack of adequate power, energy or strength required to achieve a particular task. Some antonyms of underpower include empower, strengthen, enhance, fortify, amplify, and boost. To empower means to give someone the authority, strength or power to do something. Strengthen and fortify imply making something stronger, better or more durable. Enhance means to increase the quality, value or effectiveness of something. Amplify and boost mean to increase the intensity, volume or power of something. In summary, antonyms of underpower are words that describe the ability to improve, increase, and augment existing capabilities.