- Impenetrable - Invincible - Invulnerable - 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. - Capable of being impregnated, as the egg of an animal,
or the ovule of a plant.
- Exempt from obligation - Exempt from, ... to - In reverse, duodenum might internally be protected from disease - Insusceptible - Invulnerable - Protected against a disease - Resistant