impenetrable /im-penˈi-trə-bl/

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

impenetrabilˈity noun

• flying-boat
• flying-boats
• flying bomb
• flying bombs
• flying bridge
• flying bridges
• flying buttress
• flying buttresses
• flying camp
• flying camps
• flying colours
• high words
• highwrought
• higry-pigry
• HIH
• hi-hat
• hi-hats
• hijab
• hijabs
• hijack
• hijacked
• hijacker
• hijackers
• hijacking
• hijackings