Box or barrel, extremely elegant (6)
I believe the answer is:
casket
'box' is the definition.
(I know that casket is a type of box)
'barrel extremely elegant' is the wordplay.
'barrel' becomes 'cask' (synonyms).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'elegant' with its centre removed is 'et'.
'cask'+'et'='CASKET'
'or' is the link.
(Other definitions for casket that I've seen before include "Box for jewellery, or corpse" , "Small box for holding jewellery" , "Box for jewellery or ashes" , "Small box or chest" , "Helping boost" .)