The drink with relative flavour (6)
I believe the answer is:
season
'flavour' is the definition.
(I know that flavour can be written as season)
'the drink with relative' is the wordplay.
'the drink' becomes 'sea' (old nickname for the sea).
'with' is a charade indicator (letters next to each other).
'relative' becomes 'son' (son is a kind of relative).
'sea'+'son'='SEASON'
(Other definitions for season that I've seen before include "eg.Summer" , "Add salt, pepper, spice etc" , "One of four periods" , "Spring, say" , "Add flavouring" .)