Assert someone partying wildly will lose face (4)
I believe the answer is:
aver
'assert' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for aver that I've seen before include "Maintain - state" , "Declare or insist" , "State firmly, declare" , "State decisively" , "Firmly maintain" .)