1. go off at a tangent : (说话时)突然扯到题外, 突然背离原来的途径, 突然改变行径/思想；
名词
1. 切线
A tangent is a line that touches the edge of a curve or circle at one point, but does not cross it.
2. 突然偏离原来的思路;突然离题
If someone goes off at a tangent, they start saying or doing something that is not directly connected with what they were saying or doing before.
1. ratio of the opposite to the adjacent side of a right-angled triangle
Synonym: tan
2. a straight line or plane that touches a curve or curved surface at a point but does not intersect it at that point