Stadia (6)
I believe the answer is:
arenas
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stadia</span>' is the definition.<br/ ><span class="explanation-format__explanation">('arena' can be a synonym of 'stadium')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for arenas that I've seen before include "Sites of gladiatorial combat" , "rings" , "Places for Roman shows" , "Spaces in centre of stadiums" , "Areas of endeavours" .)