Entertainment venue (6)
'entertainment venue' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arena that I've seen before include "Gladiatorial venue" , "What the Colosseum was" , "Entertainments venue" , "Stadium - battlefield" , "battlefieId" .)
(Other definitions for circus that I've seen before include "Performances in ring" , "(Show in) big top" , "Eg, Piccadilly, Oxford" , "Big top entertainment" , "Group of travelling performers" .)