Sash that's somewhat too big (3)
I believe the answer is:
obi
'sash' is the definition.
(type of Japanese sash or belt)
'somewhat too big' is the wordplay.
'somewhat' says the answer is hidden in the clue.
'OBI' can be found hidden inside 'too big'.
'that's' is the link.
(Other definitions for obi that I've seen before include "exotic waistband" , "Form of witchcraft" , "West Indian witchcraft" , "Japanese habit?" , "Sash worn on Japanese kimono" .)