The term "most unrivalled" is an example of a superlative that indicates something is beyond compare or without equal. The antonyms for this phrase would be words that express a sense of comparison and competition. Some examples of antonyms for "most unrivalled" include mediocre, average, ordinary, but these are rather mild antonyms. More powerful antonyms could be dominated, inferior, second-rate, or eclipsed. The use of antonyms is an effective tool to highlight contrast and provide a better understanding of a word's meaning. By using antonyms, writers can create a sense of tension or conflict in their writing and evoke strong emotions in their readers.