Corpulent alumnus has half of cheese (5)
I believe the answer is:
obese
'corpulent' is the definition.
('obese' can be a synonym of 'corpulent')
'alumnus has half of cheese' is the wordplay.
'alumnus' becomes 'ob' (old boy).
'has' is a charade indicator (letters next to each other).
'half of' indicates taking half.
'cheese' with half the letters taken is 'ese'.
'ob'+'ese'='OBESE'
(Other definitions for obese that I've seen before include "Very big" , "Very substantial" , "Unhealthily fat and overweight" , "Grossly overweight" , "Grossly fat" .)