Collar estimated, by the sound of it (4)
I believe the answer is:
ruff
'collar' is the definition.
(I know that ruff is a type of collar)
'estimated by the sound of it' is the wordplay.
'estimated' becomes 'rough' (I've seen this before).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'rough' is a homophone of 'RUFF'.
(Other definitions for ruff that I've seen before include "Type of collar" , "Ring of fur around neck of bird or animal" , "Starched, frilled collar" , "Extravagant collar" , "Fish; neck frill" .)