tangent

1. N-COUNT A tangent is a line that touches the edge of a curve or circle at one point, but does not cross it. 切線

2. PHRASE If someone goes off on a tangent, they start saying or doing something that is not directly connected with what they were saying or doing before. 突然離題[V and N inflect]

The conversation went off on a tangent. 談話突然偏離了正題。