Part of speech; verb modifier (6)
I believe the answer is:
adverb
This clue is a double definition.
'part of speech' is the first definition.
(adverb is a kind of part of speech)
'verb modifier' is the second definition.
(I've seen this before)
(Other definitions for adverb that I've seen before include "Term of modification" , "Action word qualifier" , ""Quickly" is one, for example" , "Modifying word (gram.)" , "Braved (anag)" .)