Big dance (4)
I believe the answer is:
prom
'big dance' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for prom that I've seen before include "Formal dance at the end of school year" , "Concert - school dance (US)" , "Henry Wood concert" , "Seaside walk (abbr.)" , "Classical music concert for which part of the audience stands" .)