Grammatical category (4)
I believe the answer is:
verb
'grammatical category' is the definition.
(verb is a kind of grammatical category)
This is all the clue.
(Other definitions for verb that I've seen before include "Part of speech" , "Word such as run, make, or do" , "Predicate of a sentance (4)" , "Maybe protest" , "Old-fashioned art, for example" .)