Living animal or plant (8)
I believe the answer is:
'living animal or plant' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for organism that I've seen before include "Individual life form" , "Living thing -- man's giro (anag)" , "Body - cell - Mao grins (anag)" , "Something alive" , "Living animal or plant" .)