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In geometry, a tangent is a straight line that touches a curve at just one point, without crossing into it. In everyday speech, though, 'go off on a tangent' is the phrase you'll hear most — it means to suddenly start talking about something that isn't really connected to the main topic.
（數學）切線；片語 go off on a tangent 表示「離題」
原始詞典資料8 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
tangentnoun/ˈtæn.d͡ʒənt/
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A straight line touching a curve at a single point without crossing it there.
- One feature of the body, which is constructed of pressed-steel members, is the contour of the sides. They are in the form of a continuous radius from the bottom side to the cant rail, and to enable flat glass windows to be fitted the side panels are pressed around the window opening, forming a tangent to the curved bodyside.
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mathematicssciencesA function of an angle that gives the ratio of the sine to the cosine, in either the real or complex numbers. Symbols: tan, tg.
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A topic nearly unrelated to the main topic, but having a point in common with it.
- I believe we went off onto a tangent when we started talking about monkeys on unicycles at his retirement party.
- “Uncle Barnaby was always father and mother to me,” Benson broke in; then after a pause his mind flew off at a tangent. “Is old Hannah all right—in the will, I mean?”
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artartsA visual interaction between two or more lines or edges that creates a perceived relationship between them, often in a way that the artist did not intend.
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entertainmentlifestylemusicA small metal blade in a clavichord that strikes the strings to produce sound.
tangentadj/ˈtæn.d͡ʒənt/
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geometrymathematicssciencesTouching a curve at a single point but not crossing it at that point.
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Of a topic, only loosely related to a main topic.
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rail-transportrailwaystransportStraight; not horizontally curved.
- The collision occurred on a two-mile stretch of tangent track.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。