Unlock to reveal (8)
I believe the answer is:
disclose
I believe this clue is a double definition.
'unlock' is the first definition.
(thesaurus)
'reveal' is the second definition.
(disclosing is a kind of revealing)
'to' acts as a link.
(Other definitions for disclose that I've seen before include "Report" , "Divulge or expose" , "Lay bare" , "Make public" , "Sold ices (anag)" .)