hermetic

Concise Oxford English Dictionary © 2008 Oxford University Press:
hermetic /həːˈmɛtɪk/

▶adjective

• 1 (of a seal or closure) complete and airtight.

• 2 insulated or protected from outside influences.

• 3 (also Hermetic) of or denoting an ancient occult tradition encompassing alchemy, astrology, and theosophy.

  ■ esoteric; cryptic.

– derivatives
hermetically adverb,
hermeticism noun.

– origin C17: from mod. L. hermeticus, from Hermes Trismegistus, the legendary founder of alchemy and astrology identified with the Greek god Hermes.