Antonyms for the word "illfitting" include words like "appropriate," "suitable," "well-suited," "well-fitting," "proper," and "well-matching." These words refer to things that fit well, are in the right size, and are right for the task or occasion. For instance, a suit that fits perfectly or a dress that is tailored to fit just right is an appropriate choice for an important event or occasion. Similarly, a pair of shoes that is the right size and style for a particular outfit is suitable for the occasion. Overall, antonyms for "illfitting" describe things that fit well, look good, and are appropriate for the situation at hand.