Smooth, as feathers (5)
I believe the answer is:
preen
'smooth as feathers' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for preen that I've seen before include "demonstrate pride" , "Maintain" , "Groom elaborately" , "Tidy and clean (plumage)" , "Titivate oneself" .)