Lifelong criminal? (5)

I believe the answer is:

felon

I'm a little stuck... Click here to teach me more about this clue!

'criminal?' is the definition.
('felon' can be a synonym of 'criminal')

'lifelong' is the wordplay.
'FELON' is hidden in amongst the letters.
But, I am not sure how this is indicated.

Can you help me to learn more?

(Other definitions for felon that I've seen before include "Wrong-doer" , "Person who has committed a serious crime" , "convict" , "Law-breaker" , "Malefactor" .)

I've seen this clue in the Evening Standard.

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