impenetrable

1 impossible to get through or into the ancient temple was surrounded by vast stretches of impenetrable jungle Synonyms impassable (also impassible), impermeable, impervious, impregnable Related Words close, compact, dense, thick, tight; compressed, condensed; sturdy, substantial, tough; firm, frozen, hard, solid, stiff; inflexible, rigid, unbending, unyielding Near Antonyms soft, squishy; bendable, elastic, flexible, giving, malleable, pliable, yielding; absorbent, porous Antonyms negotiable, passable, penetrable, permeable

2 being beyond one's powers to know, understand, or explain the mysteries of that religion are completely impenetrable to outsiders Synonyms arcane, cryptic, deep, enigmatic (also enigmatical), mysterious, inscrutable, mystic, occult, uncannyRelated Words dark, darkling, fuzzy, murky, obscure, shadowy, vague; ambiguous, equivocal; imponderable, incomprehensible, unfathomable, unintelligible, unsearchable; inexplicable, unaccountable, unexplainable; unanswerable, unknowable; metaphysical, mystical, numinous, supernatural; abstruse, esoteric, recondite; baffling, befuddling, bewildering, confounding, confusing, disorienting, mystifying, perplexing, puzzlingNear Antonyms fathomable, intelligible, understandable; apparent, clear, evident, manifest, obvious, open-and-shut, palpable, patent, perspicuous, plain, straightforward, transparent, unambiguous, unequivocal, unmistakable

3 impossible to understand the textbook's language is completely impenetrable, at least to me Synonyms incomprehensible, unfathomable, ungraspable, unintelligibleRelated Words abstruse, enigmatic (also enigmatical), esoteric, indecipherable, inscrutable, recondite, unsearchable; cryptic, darkling, deep, mysterious, mystic, oblique, obscure, occult, uncanny; unanswerable, unknowable; baffling, bewildering, confounding, confusing, mystifying, perplexing, puzzling; inconceivable, unimaginable, unthinkableNear Antonyms basic, elemental, elementary, essential, fundamental, rudimentary, underlying; easy, simple; coherent, connected, ordered, orderly, organized, systematic, systematized; clear, cogent, compelling, convincing, lucid, pellucid, perspicuous, plain, straightforwardAntonyms fathomable, intelligible, understandable

4 not allowing penetration (as by gas, liquid, or light) the container of toxic waste has an impenetrable seal to prevent leaks Synonyms tight, impermeable, imperviousRelated Words close, compact, dense, snug, thick; airtight, hermetic (also hermetical), leakproof, watertight; lightproof, soundproof, waterproofNear Antonyms absorbent, leaky, porous, unsealedAntonyms penetrable, permeable, pervious