on a tangent

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]

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.

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His campaign is likely terrified he'll get angry and defensive and like his Fox News buddy Brian Kilmeade, go off on a tangent arguing that wanting to be more like Hitler isn't such a bad thing.

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Or the way Fauci face-palmed when Trump went off on a tangent about the “deep State Department” during one of his inane daily briefings?

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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.

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

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