A fellow spy? (5)

I believe the answer is:

agent

'spy' is the definition.
(thesaurus)

'a fellow' is the wordplay.
'fellow' becomes 'gent' ('gent' can be a synonym of 'fellow'**).
'a'+'gent'='AGENT'

(Other definitions for agent that I've seen before include "One who acts for another" , "factor in Scotland" , "Representative - means" , "Vehicle" , "Sales rep" .)

I've seen this clue in The Telegraph and The Guardian.

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