Relate story that's revealing (8)
I believe the answer is:
telltale
'revealing' is the definition.
(synonyms)
'relate story' is the wordplay.
'relate' becomes 'tell' (I've seen this in another clue).
'story' becomes 'tale' (synonyms).
'tell'+'tale'='TELLTALE'
'that's' acts as a link.
(Other definitions for telltale that I've seen before include "Blabbing person" , "Informer - monitoring device" , "Betraying" , "Revealing or indicating something, like blabbermouth" , "Person who gossips or blabs secrets" .)