Defrauded teacher, easily at first (4)
I believe the answer is:
done
'defrauded' is the definition.
(do can mean to con or defraud)
'teacher easily at first' is the wordplay.
'teacher' becomes 'don' (don can mean an academic - especially at Oxbridge).
'at first' indicates taking the first letters.
The first letter of 'easily' is 'e'.
'don'+'e'='DONE'
(Other definitions for done that I've seen before include "Completed" , "Concluded (and dusted?)" , "This sort of thing is socially acceptable" , "Complete; finished" , "See 23" .)