Cunning black rat traps one primate (10)

I believe the answer is:

archbishop

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'one primate' is the definition.
(thesaurus)

'cunning black rat traps' is the wordplay.
'cunning' becomes 'arch' (I've seen this before).
'black rat traps' becomes 'bishop' (I can't explain this - if you can you should believe this answer much more).
'arch'+'bishop'='ARCHBISHOP'

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(Other definitions for archbishop that I've seen before include "Senior churchman" , "man of the church" , "ecclesiastical dignitary?" , "Senior cleric" , "primate" .)

I've seen this clue in The Independent.

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