Elaborate finishes on the onyx container with diamonds (6)
I believe the answer is:
expand
'elaborate' is the definition.
(I know that elaborate can be written as expand)
'finishes on the onyx container with diamonds' is the wordplay.
'finishes on the onyx' becomes 'ex' (I can't justify this - if you can you should believe this answer much more).
'container' becomes 'pan' (pan is a kind of container).
'with' is a charade indicator (letters next to each other).
'diamonds' becomes 'd' (abbreviation in bridge say).
'ex'+'pan'+'d'='EXPAND'
Can you help me to learn more?
(Other definitions for expand that I've seen before include "Extend in one or more directions" , "Mushroom" , "put on weight?" , "Swell" , "increasingly elaborate" .)