Post-prandial train-fender (11)

I believe the answer is:

afterdinner

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'train-fender' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'post-prandial' is the wordplay.
'post' becomes 'after' (the prefix 'post-' means 'after').
'prandial' becomes 'dinner' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'after'+'dinner'='AFTERDINNER'

Can you help me to learn more?

I've seen this clue in The Irish Independent and The Irish News.

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