- Impenetrable - Invincible - Invulnerable - Not possible to overcome mad bleeping ram - Not to be overthrown - Unassailable - Not to be stormed, or taken by assault; incapable of
being subdued; able to resist attack; unconquerable; as, an impregnable
fortress; impregnable virtue.
- Exempt - Exempt from obligation - Exempt from, ... to - In reverse, duodenum might internally be protected from disease - Insusceptible - Invulnerable - Protected against a disease