Man who gives the okay? (5)
I believe the answer is:
roger
'the okay?' is the definition.
(thesaurus)
'man who' is the wordplay.
'man' becomes 'rog'.
'who' becomes 'er' (I can't explain this - if you can you should give a lot more credence to this answer).
'rog'+'er'='ROGER'
'gives' is the link.
Can you help me to learn more?
(Other definitions for roger that I've seen before include "Casement, say" , "Radio acknowledgment" , "Jolly man" , "Man's name" , "Message received and understood!" .)