Something supposed to be secret but known to almost everyone.
Webster's New World
(dated) Information that is not widely known, despite being freely available.
Other Word Forms of Open Secret
Open Secret Sentence Examples
She slowly consulted the magnates of all I parties with apparent impartiality, and finallyadopted the course which it was an open secret she had decided upon in pectore beforehand.
On the other hand, unexpurgated copies were made in Matthew's lifetime; though the offending passages are duly omitted or softened in his abridgment of his longer work, the Historia Anglorum (written about 125 3), the real sentiments of the author must have been an open secret.
Mr Dodgson was always very fond of children, and it was an open secret that the original of "Alice" was a daughter of Dean Liddell.
It was an open secret that in some instances they disagreed with the policy they were called upon to enforce.
It was an open secret that this grave decision was not taken at the cabinet council presided over by the queen without a solemn protest by Seor Moret and the ministers of war and marine that the resources of Spain were totally inadequate for a struggle with the United States.