impregnable /im-pregˈnə-bl/

1. That cannot be captured, broken into or taken by force
2. Which cannot be overcome, unassailable

• ephelis
• ephemera
• ephemerae
• ephemeral
• ephemeralities
• ephemerality
• ephemerally
• ephemeralness
• ephemerals
• ephemeras
• ephemerid
• Ephemeridae
• ephemerides
• ephemeridian
• ephemerids
• ephemeris
• ephemeris second
• ephemerist
• ephemeris time
• ephemerists
• ephemeron
• Ephemeroptera
• ephemerous
• Ephesian
• ephialtes