Reveal unintentionally (6)
I believe the answer is:
betray
'reveal unintentionally' is the definition.
(synonyms)
This is all the clue.
(Other definitions for betray that I've seen before include "Be disloyal to like Judas" , "Expose" , "Deliver to an enemy by treachery" , "Act treacherously towards (someone)" , "shop" .)