impregnable /im-pregˈnə-bl/

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

• fulgurite
• fulgurites
• fulgurous
• fulham
• fulhams
• fuliginosities
• fuliginosity
• fuliginous
• fuliginously
• full
• full-acorned
• fullage
• full-aged
• fullages
• fullam
• fullan
• full and by
• full back
• full backs
• full beam
• full beams
• full blast
• full-blast
• full-blood
• full-blooded