tangent

n. 1 (often attrib.) Straight line, curve, or surface that meets a curve at a point, but does not intersect it. 2 ratio of two sides (other than the hypotenuse) opposite and adjacent to an acute angle in a right-angled triangle.  at a tangent diverging from a previous course or from what is relevant or central (go off at a tangent). [latin tango tact- touch]

v. t. A tangent line curve, or surface; specifically, that portion of the straight line tangent to a curve that is between the point of tangency and a given line, the given line being, for example, the axis of abscissas, or a radius of a circle produced. See Trigonometrical function, under Function.