Frank possibly has Capone's temper (6)
I believe the answer is:
anneal
'temper' is the definition.
(synonyms)
'frank possibly has capone's' is the wordplay.
'frank possibly' becomes 'anne' (Anne Frank, Holocaust victim. I am not sure about the 'possibly' bit.).
'has' means one lot of letters go next to another.
'capone' becomes 'Al' (gangster Al Capone).
'anne'+'al'='ANNEAL'
Can you help me to learn more?
(Other definitions for anneal that I've seen before include "Long angry speech" , "Toughen using heat" , "Toughen by a process of gradually heating and cooling" , "Harden by heating and cooling" , "Destress using heat" .)