Sash on brim appearing regularly (3)
I believe the answer is:
obi
'sash' is the definition.
(type of Japanese sash or belt)
'on brim appearing regularly' is the wordplay.
'appearing regularly' means one should take alternating letters.
'on'+'brim'='onbrim'
The alternating letters of 'onbrim' are 'OBI'.
(Other definitions for obi that I've seen before include "Japanese sash - African witchcraft" , "belt" , "__-Wan Kenobi of "Star Wars" - kimono sash" , "Charm used in witchcraft" , "exotic waistband" .)