Letter opposing drink (7)
I believe the answer is:
chianti
'drink' is the definition.
(I know that Chianti is a red wine)
'letter opposing' is the wordplay.
'letter' becomes 'chi' (chi is a kind of letter of the alphabet).
'opposing' becomes 'anti' (prefix meaning 'opposing').
'chi'+'anti'='CHIANTI'
(Other definitions for chianti that I've seen before include "European wine" , "I can hit for popular Italian wine" , "I can hit (anag) - alcoholic drink" , "Popular dry red wine of Tuscany" , "Dry red Italian wine" .)