Effective relation (7)
I believe the answer is:
telling
This clue is a double definition.
'effective' is the first definition.
(similar in meaning)
'relation' is the second definition.
(to relate a story is to tell it)
(Other definitions for telling that I've seen before include "relation" , "briefing" , "Striking, having noticeable effect" , "Powerful; relating" , "Powerful; informing" .)