Ring, region around end of Saturn (5)
I believe the answer is:
arena
'ring' is the definition.
(thesaurus)
'region around end of saturn' is the wordplay.
'region' becomes 'area' ('area' can be a synonym of 'region'**).
'around' indicates putting letters inside.
'end of' says to take the final letters.
The last letter of 'saturn' is 'n'.
'area' placed around 'n' is 'ARENA'.
(Other definitions for arena that I've seen before include "Central area in sports stadium" , "Part of a stadium" , "Area of combat" , "Area in centre of sports stadium" , "centre of conflict" .)