tangent

离题、岔开的话题常与 on a 连用

He went off on a tangent about his childhood pets.

他突然离题，讲起小时候养的宠物。

切线、切面数学

Draw a tangent to the circle at that point.

在那一点画出这个圆的切线。

正切数学

The tangent of forty-five degrees equals one.

四十五度的正切值等于一。

相切的、切线的数学

The line is tangent to the curve at the origin.

这条直线在原点与曲线相切。

离题、扯远口语

Sorry, I keep going off on a tangent during meetings.

抱歉，我开会时老是扯远。