1894, Alvan S. Southworth, "A Generation of the New York Bar", in Frank Leslie's Popular Monthly (later The American Magazine), Volume XXXVII, page 427,
It was an open secret in the profession at that time that Mr. Field had very explicit documentary evidence that would have made Mr. Evarts very uncomfortable had the Bar Association thrown down the gauntlet.

It is now an open secret that Gulf states have developed ties with Israel, in the absence of formal relations, including trade partnerships and security deals.

Open secret

Meaning

Noun