The phrase "most undiminished" implies that something is at its highest or strongest level, without any decrease in value or quality. Antonyms for this phrase could include "largely diminished," "substantially reduced," or "significantly weakened." These words suggest a decrease in value or quality, either through intentional or unintentional means. Other antonyms could include "partially depleted," "somewhat decreased," or "moderately weakened." These terms imply that there has been a loss of something, but not to the same extent as a complete diminishment. Overall, the antonyms for "most undiminished" convey a sense of loss or weakening of something previously considered strong or valuable.