Grammatical gender (6)
I believe the answer is:
neuter
'grammatical gender' is the definition.
(neuter is a kind of grammatical gender)
This is all the clue.
(Other definitions for neuter that I've seen before include "Tureen (anag.)" , "Of noun, neither masculine nor feminine" , "Retune (anag.)" , "Castrate" , "Neither m nor f" .)