Identifying word (4)
I believe the answer is:
noun
'identifying word' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for noun that I've seen before include "Naming word (grammar)" , "Content word for person, place, thing etc" , "Word referring to person, place or thing" , "Word identifying people, things, etc" , "Substantive word" .)