Oxford Advanced American Dictionary

Definition of tangent noun from the Oxford Advanced Learner's Dictionary

tangent

noun
tangent pronunciation English ˈtændʒənt tangent pronunciation American ˈtændʒənt
 
1 (geometry) a straight line that touches the outside of a curve but does not cross it2 (abbr. tan) (mathematics) the ratio of the length of the side opposite an angle in a right-angled triangle to the length of the side next to it compare cosine, sine
Idioms

fly/go off at a tangent

(British English) (North American English go off on a tangent) (informal) to suddenly start saying or doing something that does not seem to be connected to what has gone beforeHe never sticks to the point but keeps going off at a tangent.