Olfactory organ (4)
I believe the answer is:
nose
'olfactory organ' is the definition.
(I know that olfactory organ can be written as nose)
This is the entire clue.
(Other definitions for nose that I've seen before include "Schnozzle" , "Don't cut this off to spite your face" , "Snout" , "In-your-face" , "Olafactory organ" .)