Well, we are secret with out letter's meaning. But as for others, I know of two in the NIC that are open (there are so many NIC I am sure there are more)
NOTE: I'm getting these from the wikipedia page. I'm not divulging anyone's secrets.
Z.B.T. referred to the first letters in the Hebrew phrase "Zion Bemishpat Tipadeh", which translated means "Zion shall be redeemed with justice"
MysticCat; But one should never assume that these are the only meanings of the letters. They may be or they may not be. 
MysticCat you are correct. While the Z.B.T society meaning of the letters were not a secret to the outside world, when it was changed to a Greek-Letter Fraternity the Founders of 1898 Columbia and the Founders of 1903 CCNY establish another meaning behind the letters which was added to the oath of brotherhood that all brothers take during the initiation process. That remains a secret.
ZBT:"Honoring the Past, Celebrating the Present & Impacting the Future."
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