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

2 PHRASE 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. 突然偏离原来的思路;突然离题