Border in the Mumbles (3)
I believe the answer is:
hem
'border' is the definition.
(I've seen this before)
'in the mumbles' is the wordplay.
'in' indicates a hidden word.
'HEM' is hidden within 'the mumbles'.
(Other definitions for hem that I've seen before include "It draws attention to" , "Part of skirt" , "try to attract attention" , "A stitched border of cloth" , "Double-backed cloth border" .)