Plumage (8)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
'plumage' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for feathers that I've seen before include "Bird insulation" , "Plumage, insulation for birds" , "Possibly down" , "Plumages" , "Aids to flight" .)