Easily passes with professor coming round (5,4)
I believe the answer is:
hands down
'easily' is the definition.
(synonyms)
'passes with professor coming round' is the wordplay.
'passes' becomes 'hands' ('hand' can be a synonym of 'pass').
'with' becomes 'w' (abbreviation).
'professor' becomes 'don' (I've seen this before).
'coming round' is an insertion indicator.
'w' placed into 'don' is 'down'.
'hands'+'down'='HANDS DOWN'
(Other definitions for hands down that I've seen before include "without effort" , "with ease" , "extremely easily" , "without difficulty" , "Workers not functioning" .)