arena

Concise Oxford English Dictionary © 2008 Oxford University Press:
arena/əˈriːnə/

▶noun

• 1 a level area surrounded by seating, in which public events and entertainments are held.

• 2 a sphere of activity: he's re-entered the political arena.

– origin C17: from L. harena, arena ‘sand, sand-strewn place of combat’.