merrymaking; convivial drinking
Refers to the lively, cheerful atmosphere of a drinking party or banquet. Often used in set phrases like 酒興に乗じて (under the influence of drink).
Carried away by the merrymaking, I ended up singing.
The banquet ended in a convivial atmosphere.
Compound of 酒 (sake, alcohol) and 興 (interest, entertainment, pleasure). The exact historical derivation is uncertain, but the combination naturally conveys the idea of enjoyment arising from drinking.