Single's following previous aniseed drink (6)
I believe the answer is:
pastis
'aniseed drink' is the definition.
(I've seen this before)
'single's following previous' is the wordplay.
'single's' becomes 'is' (one**).
'following' means one lot of letters go next to another.
'previous' becomes 'past' ('past' can be similar in meaning to 'previous').
'is' after 'past' is 'PASTIS'.
(Other definitions for pastis that I've seen before include "Aniseed-flavour aperitif" , "Rectangular" , "Aniseed-flavoured aperitif" , "Alcoholic drink flavoured with aniseed" , "Aniseed aperitif" .)