Hermetic

made airtight by fusion or sealing.

not affected by outward influence or power; isolated.

( sometimes initial capital letter ) of, pertaining to, or characteristic of occult science, esp. alchemy.

( initial capital letter ) of or pertaining to Hermes Trismegistus or the writings ascribed to him.

adjective

completely sealed , impervious , sealed , shut , tight , waterproof , watertight , airtight , alchemist , mystical , occult , secret