Revelation about early tab (8)
I believe the answer is:
betrayal
'revelation' is the definition.
(thesaurus)
'about early tab' is the wordplay.
'about' indicates anagramming the letters.
'early'+'tab'='earlytab'
'earlytab' anagrammed gives 'BETRAYAL'.
(Other definitions for betrayal that I've seen before include "The crime of Judas" , "Act of disloyalty" , "Breach of trust" , "Breaking of trust" , "Act of treachery" .)