Drink to exist for queen (4)
I believe the answer is:
beer
'drink' is the definition.
(beer is a kind of drink)
'exist for queen' is the wordplay.
'exist' becomes 'be' ('be' can be a synonym of 'exist').
'for' says to put letters next to each other.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'be'+'er'='BEER'
'to' acts as a link.
(Other definitions for beer that I've seen before include "It may be 13 across-ed!" , "pint" , "Fermented malt and hops" , "Hop drink" , "Hop-flavoured drink" .)