go (off) on a tangent

go (off) on a tangent

To begin addressing or discussing a topic or topics not relevant to the main discussion. I tried to address the customer's problem, but she kept going off on a tangent and I couldn't understand what her true complaint was. In the middle of our conversation about my finances, my advisor went on a tangent about current events.
See also: go, on, tangent
Farlex Dictionary of Idioms.

go off on a tangent

Fig. to pursue a somewhat related or irrelevant course while neglecting the main subject. Don't go off on a tangent. Stick to your job. Just as we started talking, Henry went off on a tangent about the high cost of living.
See also: go, off, on, tangent
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

go off on a tangent

BRITISH, AMERICAN or

go off at a tangent

BRITISH
1. If a person or piece of writing goes off on a tangent or goes off at a tangent, they start saying or thinking something that is not directly connected with what they were saying or thinking before. Our teacher would occasionally go off on a tangent totally unrelated to the textbook. Note: Other verbs are sometimes used instead of go. The humour is often a little forced and the book's theme wanders off on a tangent now and then.
2. If someone goes off on a tangent or goes off at a tangent, they start to behave in a completely different way from before or to do something completely different from what they were doing before. I suppose I was trying to conform, but then I went off on a tangent, moving to London to study drama. Note: In geometry, a tangent is a straight line which touches a curve at one point but does not cross it.
See also: go, off, on, tangent
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • go off at a tangent
  • go off on a tangent
  • go/fly off at a tangent
  • fly off at a tangent
  • tangent
  • (off) on a tangent
  • on a tangent
  • sidetrack
  • (off) on a sidetrack
  • off on a sidetrack