Beer this thirst finally quenched (5)
I believe the answer is:
stout
'beer' is the definition.
(I've seen this before)
'this thirst finally quenched' is the wordplay.
'finally' suggests the final letters.
'quenched' becomes 'out' ('out' can be a synonym of 'quenched').
The final letters of 'this thirst' are 'st'.
'st'+'out'='STOUT'
(Other definitions for stout that I've seen before include "Portly - porter" , "tipple" , "Dark ale" , "Robust; drink" , "Portly - type of dark beer" .)