Somewhat reflective, impressionist Serafinowicz takes it easy (5)
I believe the answer is:
rests
'takes it easy' is the definition.
(I've seen this in another clue)
'somewhat reflective impressionist serafinowicz' is the wordplay.
'reflective' shows that the letters should be reversed in order.
'somewhat' says the answer is hidden in the clue.
'stser' is hidden within 'impressionist serafinowicz'.
'stser' written backwards gives 'RESTS'.
(Other definitions for rests that I've seen before include "Relaxes, sleeps" , "Takes one's ease" , "holidays" , "Relaxes; supports" , "Reposes" .)