What does hermetic mean and Where does the word “hermetic” come from?

The ibis-headed god Thoth, in Egyptian theology, was the god of wisdom, science, magic, religion, and art.

The Greeks identified him with Hermes, and he was therefore often known as Hermes Trismegistus (Hermes Thrice-greatest). He was the reputed author of the 42 books that constituted the sum of Egyptian learning, books which were therefore known as the “Hermetic Books.”

Because they dealt largely with the occult sciences, magic and alchemy, hermetic acquired the significance of “secret, hidden,” and, in one usage, “airtight.”