Assiduous (8)
I believe the answer is:
diligent
'assiduous' is the definition.
(similar in meaning)
This is the entire clue.
(Other definitions for diligent that I've seen before include "Putting care and effort into work" , "Assiduous" , "Painstaking - I tingled (anag)" , "Steady and hard-working" , "Taking trouble" .)