Rail worker Ian is champion (8)

I believe the answer is:

guardian

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'is champion' is the definition.
(thesaurus)

'rail worker ian' is the wordplay.
'rail worker' becomes 'guard' (I can't explain this - if you can you should believe this answer much more).
'guard'+'ian'='GUARDIAN'

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(Other definitions for guardian that I've seen before include "Protector or watchful angel" , "Curator" , "Paper, protector" , "Platonic leader" , "Caretaker" .)

I've seen this clue in The Sun.

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