a straight line or plane that touches a curve or curved surface at a point, but if extended does not cross it at that point

a completely different line of thought or action

Loretta's mind went off at a tangent

the trigonometric function that is equal to the ratio of the sides (other than the hypotenuse) opposite and adjacent to an angle in a right-angled triangle

(of a line or plane) touching, but not intersecting, a curve or curved surface

this curve is tangent to the average cost curve