impenetrable /im-penˈi-trə-bl/

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

impenetrabilˈity noun

impenˈetrably adverb

• upcoils
• upcome
• upcomes
• upcoming
• up-countries
• up-country
• upcurl
• upcurled
• upcurling
• upcurls
• up-current
• up-currents
• upcurved
• upcycle
• upcycled
• upcycles
• upcycling
• update
• updated
• updates
• updating
• updo
• updos
• updrag
• updragged