A dean is leading (5)

I believe the answer is:

ahead

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'is leading' is the definition.
(to lead is to go ahead)

'a dean' is the wordplay.
'dean' becomes 'head' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'head'='AHEAD'

Can you help me to learn more?

(Other definitions for ahead that I've seen before include "likely to win?" , "In the vanguard" , "Forward - in front" , "In the leading position" , "In front as in race" .)

I've seen this clue in The Mirror and The Daily Express.

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