To some extent rising cadet is a rapacious sponger (8)
I believe the answer is:
'sponger' is the definition.
(I know that sponger can be written as parasite)
'to some extent rising cadet is a rapacious' is the wordplay.
'rising' is a reversal indicator (letters written upwards in a down clue).
'to some extent' indicates a hidden word (I've seen 'extent of' mean this (I've seen this in other clues)).
'etisarap' is hidden within 'cadet is a rapacious'.
'etisarap' back-to-front is 'PARASITE'.
(Other definitions for parasite that I've seen before include "louse, say" , "Self-interested hanger-on" , "freeloader?" , "Animal that feeds off another" , "it sucks blood" .)