Short note written about part of speech (4)
I believe the answer is:
verb
'part of speech' is the definition.
(verb is a kind of part of speech in grammar)
I cannot understand how the rest of the clue works.
(Other definitions for verb that I've seen before include "Type of word indicating action" , "A word that conveys action" , "Part of speech" , "'In grammar, it denotes action (4)'" , "Predicate of a sentance (4)" .)