Open a joint in retreat for prince (8)
I believe the answer is:
maharaja
'prince' is the definition.
(maharaja is a kind of prince)
'open a joint in retreat' is the wordplay.
'open' becomes 'ajar' (similar in meaning).
'joint' becomes 'ham' (ham is a joint of meat).
'in retreat' says the letters should be written backwards.
'ajar'+'a'+'ham'='ajaraham'
'ajaraham' reversed gives 'MAHARAJA'.
'for' acts as a link.
(Other definitions for maharaja that I've seen before include "Eminent Indian" , "foreign ruler" , "Great Indian prince" , "Indian prince or king" , "Hindu prince" .)