impenetrable /im-penˈi-trə-bl/

1. Incapable of being penetrated
2. Impervious
3. Inscrutable
4. Occupying space exclusively (physics)

• pet-sits
• pet-sitter
• pet-sitters
• pet-sitting
• petted
• pettedly
• pettedness
• pettednesses
• petter
• Petter engine
• petters
• pettichaps
• petticoat
• petticoat-breeches
• petticoated
• petticoat government
• petticoats
• petticoat-tails
• pettier
• petties
• pettiest
• pettifog
• pettifogged
• pettifogger
• pettifoggeries