Party drink, big hit (5)
I believe the answer is:
punch
This could be a double definition.
'party drink' is the first definition.
(I've seen this before)
'big hit' is the second definition.
'punch' can be an answer for 'hit' (punching is a kind of hitting). I am not sure about the 'big' bit.
Can you help me to learn more?
(Other definitions for punch that I've seen before include "Sock" , "Blow with the hand - hot drink" , "striking power" , "horse to get > drink" , "Wife-beater" .)