im·pen·e·tra·bil·i·ty 
(ĭm-pĕn′ĭ-trə-bĭlĭ-tē)
(ĭm-pĕn′ĭ-trə-bĭlĭ-tē)n.
1. The quality or condition of being impenetrable.
2. The inability of two bodies to occupy the same space at the same time.
- authentic
- authentically
- authenticate
- authentication
- authenticator
- authenticity
- author
- authorial
- authoritarian
- authoritarianism
- authoritative
- authoritatively
- authoritativeness
- authority
- authorization
- authorize
- Authorized Version
- authorizer
- authorship
- autism
- autism spectrum
- autism spectrum disorder
- autist
- autistic
- autistically