impassable

impassable, impenetrable, impervious, impermeable are comparable when they mean not allowing passage through.

Impassable applies chiefly to stretches of land or water which cannot be passed over or crossed because of some insuperable difficulty or obstruction

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the river is impassable in the rainy season

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the road between here and the city is impassable since the storm blew down the trees

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this ocean of snow, which after October is impassable— Evelyn

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the gulf is the difference between the angelic and the diabolic temperament. What more impassable gulf could you have?— Shaw

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Impenetrable applies chiefly to something which is so dense or so thick that not even the thinnest shaft (as of light or air) can find its way through

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impenetrable fog

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impenetrable darkness

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this gentleman was impenetrable to ideas— Colum

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Professor Murray has . . . interposed between Euripides and ourselves a barrier more impenetrable than the Greek language— T. S. Eliot

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Often, however, impenetrable is preferred to impassable when implying an exceedingly dense growth that prevents passage

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an impenetrable thicket

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an impenetrable forest

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Impervious, which implies impenetrability, applies basically to substances or materials which have been so finished or treated as to make them impenetrable (as to air, water, or sound waves)

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no surface coating has ever been found which is impervious to sun, wind and rain— Furnas

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When applied to persons or their minds or hearts, impervious usually implies complete resistance to anything that would affect them for better or worse

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impervious to threats or prayers or tears— Hewlett

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we become impervious to new truth both from habit and from desire— Russell

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so soaked with the preserve "good form" that we are impervious to the claims and clamor of that ill-bred creature—life!— Galsworthy

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Impermeable implies impenetrability, whether natural or artificially acquired, by a liquid or a gas and incapacity for becoming soaked or permeated; the term applies chiefly to substances (as some clays) which do not absorb water, to cloths treated so as to be rainproof, or to materials which do not admit the passage of air, light, gas, or water

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osmo-regulation in the eel is achieved by an impermeable outer covering of slime— Dowdeswell

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impermeable rocks

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gas pipes should be made of an impermeable metal

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impermeable roofing

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he was not drunk, since the resilient composition of which his nerves were made was almost impermeable to alcohol— West

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Antonyms: passable