Five in pool session replacing fellow's drink (7)
I believe the answer is:
aquavit
'drink' is the definition.
(aquavit is a kind of drink)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for aquavit that I've seen before include "Scandinavian flavoured spirit" , "strong drink" , "The Swedish drink" , "An alcoholic spirit originally from Scandinavia" .)