Approximal refers to something that is close or adjacent, often used in dentistry to describe the space between two teeth. The antonym for this word would be distant or remote. When referring to the teeth, the antonyms could be separated or far apart. Another possible antonym could be precise, as approximal implies an estimation or approximation rather than an exact measurement. The opposite of approximal could also be denoted by the terms disconnected or disjointed, meaning not connected or distant in space or relationship. Overall, the antonyms for approximal depend on the context in which the word is used.