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3. on a tangent

on a tangent

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(off) on a tangent

suddenly dealing with a completely different matter We were talking about gas prices and you went off on a tangent about your vacation plans.

See also: on, tangent

on a tangent

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 fly off or go off on a tangent , 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]

See also: on, tangent