Pair out on river for drink (7)
I believe the answer is:
campari
'for drink' is the definition.
(I've seen this before)
'pair out on river' is the wordplay.
'out' indicates an anagram (out can mean wrong or inaccurate).
'on' indicates putting letters inside (as in clothing 'on' a person).
'river' becomes 'cam' (river in Cambridge, England).
'pair' anagrammed gives 'pari'.
'pari' placed around 'cam' is 'CAMPARI'.
(Other definitions for campari that I've seen before include "Pinkish aperitif" , "Mildly bitter aperitif, often drunk with soda" , "Red, bitter-sweet Italian aperitif" , "bitter drink" .)