1. (a.) Incapable of being penetrated or pierced; not admitting the passage of other bodies; not to be entered; impervious; as, an impenetrable shield.
2. (a.) Having the property of preventing any other substance from occupying the same space at the same time.
3. (a.) Inaccessible, as to knowledge, reason, sympathy, etc.; unimpressible; not to be moved by arguments or motives; as, an impenetrable mind, or heart.
Thesaurus Entries
Greek to one, ambiguous, arcane, beyond reach, beyond understanding, cabalistic, close, close-knit, close-textured, close-woven, closed forever to, closed to, compact, compacted, compressed, concentrated, concrete, condensed, congested, consolidated, crammed, crammed full, crowded, dense, exuberant, firm, flourishing, gluey, gross, hard, heavy, holeproof, impassable, impermeable, impervious, impregnable, inaccessible, inarticulate, incognizable, incoherent, incomprehensible, incontestable, indomitable, inexpugnable, inscrutable, insuperable, invincible, inviolable, invulnerable, irresistible, jam-packed, jammed, jungled, jungly, lost to, lush, luxuriant, massive, mystic, nonporous, nonpuncturable, numinous, out of reach, overgrown, overpowering, overrun, overwhelming, packed, past comprehension, punctureproof, rambling, rank, resistless, riotous, serried, solid, substantial, thick, thick-growing, thickset, un-come-at-able, unaccessible, unaccountable, unapproachable, unassailable, unattainable, unavailable, unbeatable, unconnected, unconquerable, undiscoverable, unfathomable, ungettable, ungraspable, unguessed, unintelligible, unknowable, unobtainable, unpassable, unperforable, unpierceable, unprocurable, unreachable, unsearchable, unsecurable, unsubduable, unsurmountable, unweeded, unyielding, viscid, viscose, viscous, weed-choked, weed-ridden, weedy
