Impermeable

Part of speech: adjective

Pronunciation: /ɪmˈpɜːmɪəbəl/

Definitions

1. Not permitting the passage of liquids or gases, effectively blocking any flow through the material
2. Acting as a barrier that prevents fluids or air from crossing or seeping into the substance
3. Being resistant to penetration by moisture or air so that nothing can pass through

Etymology: "Impermeable" is a straightforward formation: the prefix "im-", meaning "not", attached to "permeable," which itself comes from the Latin "permeare," to pass through. The English word thus means "not able to be passed through," and it has been built on the same pattern that gives us "impossible" or "immovable." French has the same word, "imperméable," which passed into English from Latin "impermeābilis," built from "im-" and "permeābilis" (permeable). The English form is most likely a direct borrowing or an independent parallel formation from these Latin roots, so the two languages share a root rather than one simply copying the other. Its everyday sense of keeping out water and air, as in an "impermeable membrane," grew out of this literal meaning of being impassable to something moving through.

Synonyms: impenetrable, waterproof

Antonyms: permeable, porous