Hermetical

[hur-met-ik] /hɜrˈmɛt ɪk/

adjective
1.
made airtight by fusion or sealing.
2.
not affected by outward influence or power; isolated.
3.
(sometimes initial capital letter) of, relating to, or characteristic of occult science, especially alchemy.
4.
(initial capital letter) of or relating to Hermes Trismegistus or the writings ascribed to him.
/hɜːˈmɛtɪk/
adjective
1.
sealed so as to be airtight
2.
hidden or protected from the outside world
/hɜːˈmɛtɪk/
adjective
1.
of or relating to Hermes Trismegistus or the writings and teachings ascribed to him
2.
of or relating to ancient science, esp alchemy
3.
esoteric or recondite
adj.

c.1600 (implied in hermetically), “completely sealed,” also (1630s) “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.

hermetic her·met·ic (hər-mět’ĭk) or her·met·i·cal (-ĭ-kəl)
adj.
Completely sealed, especially against the escape or entry of air.
her·met’i·cal·ly adv.