Fellow turning up gets gesture of acceptance (3)
I believe the answer is:
nod
'gesture of acceptance' is the definition.
(I've seen this before)
'fellow turning up' is the wordplay.
'fellow' becomes 'don' (both can mean an academic).
'turning up' is a reversal indicator.
'don' in reverse letter order is 'NOD'.
'gets' acts as a link.
(Other definitions for nod that I've seen before include "overlook something" , "Go to sleep in this land" , "may get gesture of approval" , "Brief bowing gesture" , "Signal with the head" .)