Dine out, breaking diet if discovered (10)
I believe the answer is:
identified
'discovered' is the definition.
('identify' can be a synonym of 'discover')
'dine out breaking diet if' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'breaking' is an anagram indicator.
'dine' with letters rearranged gives 'iden'.
'diet'+'if'='dietif'
'dietif' with letters rearranged gives 'tified'.
'iden'+'tified'='IDENTIFIED'
(Other definitions for identified that I've seen before include "Put one's finger on" , "Given name" , "Recognised, named" , "Pointed out; made known" , "Recognized" .)