invulnerable,"['airtight ', 'airtight ', 'bombproof ', 'shellproof ', 'defendable ', 'defensible ', 'entrenched ', 'impregnable ', 'inviolable ', 'secure ', 'strong ', 'unassailable ', 'unattackable ', 'tight ', 'untouchable ', 'protected ', 'secure ', 'safe ', 'secure ', 'unconquerable ', 'vulnerable ']"