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.
Derivatives:
impenetrability n. impenetrableness n. impenetrably adv.
Etymology: ME f. F imp{eacute}n{eacute}trable f. L impenetrabilis (as IN-(1), PENETRATE)