The antonyms for the word "most strengthened" would be weakened, debilitated or undermined. When something is weakened, it has lost its strength or vigor. Debilitated refers to something that has been weakened to the point of being unable to function properly. When something is undermined, its foundation or structure has been weakened, leading to a loss of strength. These antonyms are opposite in meaning to "most strengthened," which indicates that something has been made stronger or more powerful. In contrast, the antonyms imply a loss or decrease in strength.