The term "most ill-fitted" refers to something that is unsuitable or inappropriate. Its antonyms could be phrases like "highly apt" or simply "perfectly fitting". Other antonyms may include terms like "well-suited", "well-matched", "properly matched" or "well-adjusted" which all refer to the suitability of something to a given purpose. These words are usually used when talking about clothing, relationships, objects, or activities. Opposing words for "most ill-fitted" could also be "matching", "compatible", "harmonious", and "appropriate". Using the appropriate and most fitting word when describing something is key to effective communication.