Adult with secret, first to be outed earlier (8)
I believe the answer is:
anterior
'earlier' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for anterior that I've seen before include "Located before, in time or place" , "Previous, to the fore" , "Nearer the front or the head" , "Towards the front" , "Nearer the front; earlier" .)