on a tangent

Idioms  

1. On a sudden digression or change of course, as in The professor's hard to follow; he's always off on a tangent. This phrase often occurs in the idioms, as in The witness was convincing until he went off on a tangent. This expression alludes to the geometric tangent—a line or curve that touches but does not intersect with another line or curve. [Second half of 1700s]

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Example Sentences

"Some of them will run straight, some of them will not start at all, some of them will go off on a tangent or bite each other," she explained.

From BBC • Apr. 19, 2025

Maher tried to ask a follow-up after Conway went on a tangent about Hillary Clinton, whose presidential campaign ended almost eight years ago, before being interrupted.

From Salon • May 4, 2024

I had a phone call with an FBI agent and the U.S. attorney in San Diego on a tangent for this case.

From Slate • Feb. 24, 2024

I don’t mean to go off on a tangent, but I noticed that “functions modeling” was also included in the offending textbooks in Florida.

From Washington Post • Apr. 25, 2022

“But that is quite enough wondering about that,” she told herself, for they had arrived at the gates of the palace, and it was no time to go off on a tangent.

From "The Hidden Gallery" by Maryrose Wood