Word that qualifies an action (6)
I believe the answer is:
adverb
'word that qualifies an action' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for adverb that I've seen before include "Rarely is one" , "Action word qualifier" , "Word that modifies something other than a noun" , "Word such as "quickly"" , "fast, maybe?" .)