Thick scarf (7)
I believe the answer is:
muffler
'thick scarf' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for muffler that I've seen before include "Thick scarf - silencer (US)" , "Kind of scarf" , "Wrap or scarf worn round the neck" , "Sound deadener" , "Warming garment" .)