adj. belonging in any way to the the beliefs current in the Middle Ages under the name of Hermes, the Thrice Great: belonging to magic or alchemy, magical: perfectly close.—adv.
Chambers's Twentieth Century Dictionary (1908)
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1. Of, pertaining to, or taught by, Hermes Trismegistus; as, hermetic philosophy. Hence: Alchemical; chemic. The alchemists, as the people were called who tried to make gold, considered themselves followers of Hermes, and often called themselves Hermetic philosophers.
2. Of or pertaining to the system which explains the causes of diseases and the operations of medicine on the principles of the hermetic philosophy, and which made much use, as a remedy, of an alkali and an acid; as, hermetic medicine.
3. Made perfectly close or air-tight by fusion, so that no gas or spirit can enter or escape; as, an hermetic seal.
For the mistress of Tansonville knew that April, even an ice-bound April, was not barren of flowers, that winter, spring, summer are not held apart by barriers as hermetic as might be supposed by the town-dweller who, until the first hot day, imagines the world as containing nothing but houses that stand naked in the rain.
Marcel Proust. In Search of Lost Time [volume 2]
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This, then, was the hermetic vision of her which I had locked in
Vladimir Nabokov. Lolita
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What do you think really of that hermetic crowd, the opal hush poets: A. E. the mastermystic? That Blavatsky woman started it. She was a nice old bag of tricks.