Partial to Percy Stevenson's pussy, Bump (4)
I believe the answer is:
cyst
'bump' is the definition.
(thesaurus)
'partial to percy stevenson's pussy' is the wordplay.
'partial to' indicates the answer is hidden within the clue (the answer forms part of the clue).
'CYST' can be found hidden inside 'percy stevensons pussy'.
(Other definitions for cyst that I've seen before include "pouch" , "Small sac in body (that may form abnormal lump)" , "Abnormal closed sac in a body" , "Sac in the body containing liquid secretion" , "Bag of fluid" .)