Bitterly reproach perjurer for going back (4)

I believe the answer is:

rail

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'bitterly reproach' is the definition.
I know that 'bitterly' relates to this answer. I also know that both the answer and definition are singular nouns

I can't explain the rest of the clue.

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(Other definitions for rail that I've seen before include "Water bird; barrier" , "Line" , "Track - complain - bird" , "Bar of rolled steel" , "Scold, berate" .)

I've seen this clue in The Irish Independent.

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