Impenetrable
/ɪmˈpɛnətɹəbəl/
adjective
Not penetrable.
“The fortress is impenetrable, so it cannot be taken.”
Incomprehensible; fathomless; inscrutable.
“Business jargon makes this document impenetrable, I can't understand it.”
Opaque; obscure; not translucent or transparent.
“When night falls, she cloaks the world in impenetrable darkness.”
Synonyms: impregnable, unfathomable