impenetrable

adjective

1 the ships had impenetrable armoured plating:

impervious, impermeable, solid, dense, thick, hard, unyielding, unbreakable, indestructible, puncture-proof, unpierceable, resistant;

invulnerable, impregnable, inviolable, unattackable, unassailable;

waterproof, closed, sealed, hermetically sealed, tight;

secure, safe, fortress-like.

▷antonyms permeable; vulnerable.

2 a dark, impenetrable forest:

impassable, unpassable, inaccessible, unnavigable, untraversable, pathless, trackless, untrodden;

dense, thick, overgrown, jungly, jungle-like;

archaic thickset.

▷antonyms accessible; sparse.

3 an impenetrable clique:

exclusive, closed, secretive, secret, private;

restrictive, restricted, limited;

rare discriminative.

▷antonyms open.

4 these statistics can seem impenetrable and tedious:

incomprehensible, impossible to understand, unfathomable, fathomless, inexplicable, unintelligible, unclear, baffling, bewildering, puzzling, perplexing, confusing, abstruse, obscure, opaque, recondite, inscrutable, mysterious, cryptic, Delphic;

complex, complicated, difficult, hard;

archaic wildering;

rare insolvable.

▷antonyms clear.

impenetrable Oxford Dictionary of English