A sign of diminished dash? (5)

I believe the answer is:

minus

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'a sign' is the definition.
(I know that minus is a type of sign)

I don't understand how the rest of the clue works.

(Other definitions for minus that I've seen before include "'Take away' sign" , "(Of temperature) below zero" , "Negative sign - negative thing" , "Negative arithmetic operation" , "Deprived of" .)

I've seen this clue in the Evening Standard.

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