A tangent is an entirely different topic or direction. When you want a break from geometry class, you might ask your teacher about his hobby of woodworking, a topic that's always good for a ten-minute tangent.

Tangent is mainly a mathematical term, meaning a line or plane that touches a curved surface but doesn't intersect it. The non-mathematical meaning of tangent comes from this sense of barely touching something: when a conversation heads off on a tangent, it's hard to see how or why it came up. When talking about history, someone suddenly brings last night's basketball game? Definitely a tangent.

Definitions of tangent

n a straight line or plane that touches a curve or curved surface at a point but does not intersect it at that point

Type of:
straight line
a line traced by a point traveling in a constant direction; a line of zero curvature

n ratio of the opposite to the adjacent side of a right-angled triangle

Type of:
circular function, trigonometric function
function of an angle expressed as a ratio of the length of the sides of right-angled triangle containing the angle