Ill formed means something that is not properly constructed or shaped. The opposite of ill formed is well-formed, which means that the structure or shape is correct and precise. Whereas ill-formed conveys negativity and faultiness, well-formed denotes positivity and excellence. Good structure and shape give a sense of perfection and completeness to an object, idea, or organism. Therefore, it is essential to have a well-formed plan, a well-formed opinion, a well-formed body, or a well-formed sentence to achieve success and convey the right message. In summary, the antonym for ill formed is well-formed, which highlights excellence, precision, and positivity.