Drunken rogue left university and became a monster (4)
I believe the answer is:
ogre
'monster' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ogre that I've seen before include "Man-eating monster of fairy tales" , "stern one who inspires fear" , "Cruel giant of folklore" , "Jack's giant perhaps" , "Ugly giant" .)