French main? Opening unopened wine! (6)
I believe the answer is:
merlot
'wine' is the definition.
(I've seen this before)
'french main? opening unopened' is the wordplay.
'french main?' becomes 'mer' ('sea' in French - the main can mean the sea).
'opening' becomes 'slot' (slot is a kind of opening).
'unopened' means to remove the first letter (without opening letter).
'slot' with its first letter removed is 'lot'.
'mer'+'lot'='MERLOT'
(Other definitions for merlot that I've seen before include "Strange wine made from elm rot" , "Black wine grape" , "French variety of grape" , "Grape makes elm rot" , "Black grape variety" .)