hermetic

hermetic \hur-MET-ik\, adjective:

1. closed tightly; airtight
2. obscure; magical

French control of the border in barring foreign volunteers is so hermetic that Mrs. Stattelman, a former Red Cross nurse who served with the French Army during the World War and is a Swiss citizen, 60 years old, was refused a passport into Spain both at Toulouse and Bordeaux.
-- Ernest Hemingway, Hemingway Finds France is Neutral, New York Times, March 17, 1937

Even the famous obscurity of some of his poetry seems driven by this desire always to be seen setting forth; what is a hermetic idiom but the sign of a new language getting itself under way?
-- Nicholas Jenkins, A Life of Beginnings, New York Times, January 4, 1998

by 1663, "completely sealed," also (1637) "dealing with occult science or alchemy," from Latin hermeticus, from Greek Hermes, god of science and art, among other things, identified by Neoplatonists, mystics, and alchemists with the Egyptian god Thoth as Hermes Trismegistos "Thrice-Great Hermes," who supposedly invented the process of making a glass tube airtight (a process in alchemy) using a secret seal.