tangential

A line that is tangent to a curve at a point on the curve is a line that just barely touches the curve at that point. So the point in question is on the line but its nearest neighbors are not. An acceleration that is directed along that line is referred to as a tangential acceleration.

Note: A line that is tangent to a circle at a point is also perpendicular to the radius of the circle that extends from the center of the circle to that point.

Note: The velocity of any particle moving along a curved path is at all instants tangent to the path. Thus a particle's velocity is always its tangential velocity. Hence, as regards velocity, the adjective "tangential" is seldom if ever used.