Part of Prospero learned (4)
I believe the answer is:
role
'part' is the definition.
(eg a theatrical role)
'of prospero learned' is the wordplay.
'of' indicates the answer is hidden within the clue.
'ROLE' can be found hidden inside 'prospero learned'.
(Other definitions for role that I've seen before include "Part (in drama)" , "Impersonation" , "Part played (in life?)" , "A part of lore" , "Duty" .)