Secant
in geometry, a straight line cutting a curve in two or more points. If a secant line be revolved about one of its points of secancy till the other point of secancy coincides with it, the secant becomes a tangent. If it be still further revolved, it again becomes a secant on the other side; hence, a tangent to a curve, at any point, is a limit of all secants through that point. A secant plane is one which intersects a surface or solid.
In trigonometry, a straight line drawn from the center of a circle through the second extremity of an arc, and terminating in a tangent to the first extremity of the arc.