Claret mixed with English syrup (7)
I believe the answer is:
treacle
'syrup' is the definition.
(I know that treacle is a type of syrup)
'claret mixed with english' is the wordplay.
'mixed with' indicates an anagram.
'english' becomes 'e' (abbreviation).
'claret' with its letters mixed up with 'e' makes 'TREACLE'.
(Other definitions for treacle that I've seen before include "Dark viscous 11" , "Golden syrup" , "Contrived sentimentality - sticky substance" , "Sweet, black viscous substance" , "Electra (anag)" .)