impregnable /im-pregˈnə-bl/

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

impregnabilˈity noun

• suboperculum
• suboptimal
• suborbital
• suborder
• suborders
• subordinacy
• subordinal
• subordinaries
• subordinary
• subordinate
• subordinate clause
• subordinate clauses
• subordinated
• subordinated debt
• subordinately
• subordinateness
• subordinatenesses
• subordinates
• subordinating
• subordinating conjunction
• subordinating conjunctions
• subordination
• subordinationism
• subordinationist
• subordinationists