Lear squiffy in court: it's the wine (6)
I believe the answer is:
claret
'the wine' is the definition.
(claret is a kind of wine)
'lear squiffy in court' is the wordplay.
'squiffy' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'court' becomes 'ct' (abbreviation used in road names).
'lear' anagrammed gives 'lare'.
'lare' inserted into 'ct' is 'CLARET'.
'it's' is the link.
(Other definitions for claret that I've seen before include "Dark red Bordeaux wine" , "English word for red Bordeaux wine" , "vessel might contain this?" , "in one's veins?" , "Wine from the Bordeaux region" .)