Main Entry: her·met·ic

Pronunciation: \(ˌ)hər-ˈmet-ik\

Function: adjective

: being airtight or impervious to air

—her·met·i·cal·ly \-i-k(ə-)lē\ adverb

Her·mes Tris·me·gis·tus, \ˈhər-(ˌ)mēz-ˌtris-mə-ˈjis-təs\ Greek mythological character. Hermes Trismegistus was identified by the Greeks with the Egyptian god Thoth. To him was ascribed authorship of various works on astrology, magic, alchemy, and medicine. It was also believed that he had invented a magic seal to keep vessels airtight, and from his name the adjective hermetic meaning airtight was derived.