Bitterly reproach false witness for standing up (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 don't understand how the remainder of the clue works.

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(Other definitions for rail that I've seen before include "Part of train track" , "wader" , "Perch" , "Bar - marsh bird" , "Fulminate - wading bird" .)

I've seen this clue in The Irish Independent.

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