adj. 1 that cannot be penetrated. 2 inscrutable, unfathomable. 3 inaccessible to ideas, influences, etc. 4 Physics (of matter) having the property such that a body is incapable of occupying the same place as another body at the same time. impenetrability n. impenetrableness n. impenetrably adv.
[ ME f. F impénétrable f. L impenetrabilis (as IN-(1), PENETRATE) ]