What term describes movement toward the thumb side of the hand?

The term that describes movement toward the thumb side of the hand is radial deviation. This motion occurs at the wrist joint when the hand moves toward the radius bone, which is located on the thumb side of the forearm. During radial deviation, the thumb is effectively brought closer to the forearm and the pinky moves away, resulting in a sideways motion of the wrist.

In contrast, ulnar deviation refers to movement toward the ulnar bone, which is on the opposite side of the thumb, toward the little finger. Adduction describes the movement of a body part toward the midline of the body, and while it can apply to the fingers uniting toward the midline, it does not specifically address the movement toward the thumb side. Opposition is a specific movement of the thumb that allows it to touch the tips of the other fingers, which is different from the lateral movement described in the question.