Couple allowed to form band (8)
I believe the answer is:
bracelet
'band' is the definition.
(bracelet is a kind of band)
'couple allowed' is the wordplay.
'couple' becomes 'brace' ('brace' can be a synonym of 'couple'**).
'allowed' becomes 'let' (I've seen this before).
'brace'+'let'='BRACELET'
'to form' is the link.
(Other definitions for bracelet that I've seen before include "Ornamental band worn on wrist" , "Arm band" , "Bangle" , "Wrist, arm adornment" , "Arm jewellery" .)