Final answer:
The correct dental term for the tooth surface farthest from the midline is 'distal'.
Step-by-step explanation:
The proper dental term for describing a tooth surface that is farthest from the midline is distal. Therefore, the correct answer to the question, "Which of the following is a proper dental term for describing a tooth surface?" is d. Distal—farthest from the midline. The term mesial refers to a surface that is nearest the midline of the set of teeth, and it is not the correct answer in this case.