Emily Dickinson Lexicon

impregnable, adj. [Fr.] (webplay: assault, fortress, moved, taken).

1. Impenetrable; imperceptible; [fig.] invisible; hidden; not seeable; not revealed; [metaphor] puzzling; unclear; incomprehensible.
2. Unassailable; inviolable; intact; not reducible; [fig.] divine; sacrosanct; eternal; everlasting.
3. Invincible; incorruptible; [fig.] everlasting; not really subject to death.
4. Not subject; not subservient; not amenable; not yielding; not succumbing; not susceptible.