Rush drink, first of revelry (4)
I believe the answer is:
tear
'rush' is the definition.
(tearing is a kind of rushing)
'drink first of revelry' is the wordplay.
'drink' becomes 'tea' (tea is a drink).
'first of revelry' becomes 'r' (1st letter of 'revelry').
'tea'+'r'='TEAR'
(Other definitions for tear that I've seen before include "Rip, sever roughly" , "Shred" , "Lachrymal fluid" , "A drop of sadness" , "charge" .)