The type of synovial joint that primarily permits rotational movement is the Pivot joint.

Explanation:
Synovial joints are classified based on the shape of their articulating surfaces and the movements they allow. Among these:
- The Hinge joint allows movement mainly in one plane, such as flexion and extension (e.g., elbow joint).
- The Saddle joint permits movement in two planes — flexion-extension and abduction-adduction — providing a wide range of motion but not primarily rotation (e.g., carpometacarpal joint of the thumb).
- The Condyloid joint also allows movement in two planes, including flexion-extension and abduction-adduction, but limited rotation (e.g., wrist joint).
- The Pivot joint is uniquely adapted to allow rotation around a single longitudinal axis. This rotational movement is seen when the radius rotates around the ulna at the proximal radioulnar joint, enabling pronation and supination of the forearm.

Thus, when asked which synovial joint primarily permits rotation, the correct answer is Pivot joint.

Reference: Gray's Anatomy, 41st Edition, Volume 1, Chapter 6: Joints, p. 745