The fellow returns to show agreement
I believe the answer is:
nod
'show agreement' is the definition.
(I've seen this in another clue)
'the fellow returns' is the wordplay.
'the fellow' becomes 'don' (both can mean an academic).
'returns' shows that the letters should be reversed in order.
'don' written backwards gives 'NOD'.
'to' is the link.
(Other definitions for nod that I've seen before include "The Land of ... lay east of Eden" , "sleepy land" , "Drop the head" , "overlook something" , "Gesture of agreement" .)