The word "un-diminished" means not reduced or decreased in its quality, intensity, or quantity. The antonyms of "un-diminished" are decreased, diminished, reduced, weakened, and lessened. These words imply a considerable loss of the original state or form of the object. If something is "diminished," it has lost some of its significance or importance. "Reduced" suggests that the amount or size of something has been decreased. "Weakened" relates to the decline in the strength or power of something. In short, the antonyms of "un-diminished" suggest a decline or deterioration in a specific aspect or the whole item itself.