Isn't idle (4)
I believe the answer is:
acts
'isn't idle' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for acts that I've seen before include "appears (eight in a series may be found)" , "bands, comedians, etc" , "Cast down by deeds" , "Is effective" , "New Testament book immediately following the Gospels" .)