tangential velocity

…distribution of proper motions and tangential velocities (the speeds at which stellar objects move at right angles to the line of sight) of stars near the Sun.

…velocity of the planet is tangent to the orbit. In the absence of gravity, the planet would obey the law of inertia (Newton’s first law) and fly off in a straight line in the direction of the velocity at constant speed. The force of gravity serves to overcome the inertial…

74 equals the tangential velocity, V_T, in kilometres per second in the plane of the celestial sphere.