Let slip clergyman brewed ale (6)
I believe the answer is:
reveal
'let slip' is the definition.
(thesaurus)
'clergyman brewed ale' is the wordplay.
'clergyman' becomes 'rev' (I've seen this before).
'brewed' indicates an anagram.
'ale' anagrammed gives 'eal'.
'rev'+'eal'='REVEAL'
(Other definitions for reveal that I've seen before include "Show, uncover" , "Make disclosure" , "Expose or display" , "Leaver (anag.)" , "Spill beans" .)