impervious

1 not allowing penetration (as by gas, liquid, or light) the material for this coat is supposed to be impervious to rain Synonyms impenetrable, impermeable, tightRelated Words close, compact, dense, snug, thick; airtight, hermetic (also hermetical), leakproof, watertight; lightproof, soundproof, waterproofNear Antonyms absorbent, leaky, porous, unsealedAntonyms penetrable, permeable, pervious

2 impossible to get through or into the rain forest is impervious to all but the most dedicated explorers Synonyms impassable (also impassible), impermeable, impenetrable, impregnableRelated Words close, compact, dense, thick, tight; compressed, condensed; sturdy, substantial, tough; firm, frozen, hard, solid, stiff; inflexible, rigid, unbending, unyieldingNear Antonyms soft, squishy; bendable, elastic, flexible, giving, malleable, pliable, yielding; absorbent, porousAntonyms negotiable, passable, penetrable, permeable