Point out prime realm (6)
I believe the answer is:
empire
'realm' is the definition.
(I know that empire is a type of realm)
'point out prime' is the wordplay.
'point' becomes 'e' (compass point).
'out' is an anagram indicator.
'prime' is an anagram of 'mpire'.
'e'+'mpire'='EMPIRE'
(Other definitions for empire that I've seen before include "Sovereign state" , "Kingdom" , "Supreme sovereignty" , "See 5" , "Widespread political or industrial organisation" .)