Jelly shot follows a third of absinthe (5)
I believe the answer is:
aspic
'jelly' is the definition.
(I know that aspic is a type of jelly)
'shot follows a third of absinthe' is the wordplay.
'shot' becomes 'pic' (I've seen this in another clue).
'follows' means one lot of letters go next to another.
'third of absinthe' becomes 's' (crd letter of 'absinthe').
'a'+'s'='as'
'pic' after 'as' is 'ASPIC'.
(Other definitions for aspic that I've seen before include "Jelly made with fish or meat stock" , "Ending of Marlowe's thriller" , "Clear meat or fish jelly" , "Savoury jelly for coating meats and eggs" , "stock production" .)