Boss with yen for learning (5)
I believe the answer is:
study
'for learning' is the definition.
(study is a kind of learning)
'boss with yen' is the wordplay.
'boss' becomes 'stud' (both can mean a metal decoration).
'with' is a charade indicator (letters next to each other).
'yen' becomes 'y'.
'stud'+'y'='STUDY'
(Other definitions for study that I've seen before include "Scrutinize" , "Read: den" , "Revise" , "Learn; den" , "Read; examine" .)