Lecturer’s indication of agreement written about (3)
I believe the answer is:
don
'lecturer's' is the definition.
(don can mean an academic)
'indication of agreement written about' is the wordplay.
'indication of agreement' becomes 'nod' (a nod indicates agreement).
'written about' says the letters should be written in reverse.
'nod' reversed gives 'DON'.
(Other definitions for don that I've seen before include "Put on; college teacher" , "Put on; man's name" , "Spanish gentleman" , "Bradman, the ---" , "Spanish nobleman" .)