adj. (also hermetical) 1 with an airtight closure. 2 protected from outside agencies. 3 a of alchemy or other occult sciences (hermetic art). b esoteric. hermetic seal an airtight seal (orig. as used by alchemists). hermetically adv. hermetism n.
[ mod.L hermeticus irreg. f. Hermes Trismegistus thrice-greatest Hermes (as the founder of alchemy) ]