Discredit wife leaving old prison (6)

I believe the answer is:

negate

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'discredit' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for negate that I've seen before include "Cause to have no effect" , "Nullify - deny the existence of" , "Contradict" , "Deny the truth of" , "Discredit" .)

I've seen this clue in The Sun.

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