The word "un-strengthening" means the opposite of strengthening or to weaken. Its antonyms could be words like fortifying, bolstering, empowering, reinforcing, invigorating, revitalizing and enhancing. Fortifying suggests making stronger or more secure, while bolstering implies lending support or adding strength. Empowering means giving authority or power to act. Reinforcing suggests strengthening something by adding more material or support. Invigorating means to add energy, excitement, or freshness. Finally, revitalizing suggests restoring, renewing or bringing back to life, while enhancing refers to improving, increasing or making something better in quality or value.