Big top entertainment (6)
I believe the answer is:
circus
'big top entertainment' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for circus that I've seen before include "(Show in) big top" , "lively scene" , "Trvelling company of entertainers, usually with animals" , "One's named Oxford" , "Eg, Piccadilly, Oxford" .)