Entitlement to drink is absolute! (9)
I believe the answer is:
downright
'absolute' is the definition.
(thesaurus)
'entitlement to drink' is the wordplay.
'entitlement' becomes 'right' (I've seen this before).
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'drink' becomes 'down' (downing is a kind of drinking).
'right' after 'down' is 'DOWNRIGHT'.
'is' acts as a link.
(Other definitions for downright that I've seen before include "rank" , "Frank" , "Absolutely!" , "Utter, complete" , "Unequivocally" .)