impenetrable /im-penˈi-trə-bl/

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

• flatlands
• flatlet
• flatlets
• flatline
• flatlined
• flatliner
• flatliners
• flatlines
• flatling
• flatlings
• flatlining
• flatlong
• flatly
• flatmate
• flatmates
• flatness
• flatnesses
• flat out
• flatpack
• flatpacks
• flat-panel
• flat playing field
• flat race
• flat races
• flat racing