noun
[ sing. ] ( informal ) something that seems to prove that sb has done sth wrong or illegal :
This memo could be the smoking gun that investigators have been looking for.
noun
[ sing. ] ( informal ) something that seems to prove that sb has done sth wrong or illegal :
This memo could be the smoking gun that investigators have been looking for.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005