What is another word for be proof?
Pronunciation: [biː pɹˈuːf] (IPA) 
To be proof means to be resistant to something or immune to its effects. Some synonyms for this phrase include impervious, invulnerable, immune, unassailable, unbreakable, indestructible, and impenetrable. These words all suggest strength and resistance against any external force that might seek to penetrate or damage the thing that is being described as proof. Other synonyms might include safe, secure, untouchable, or unaffected. Whether used to describe a physical object or a mental or emotional state, to be proof suggests a certain level of strength and resilience that can repel or withstand any challenge or threat.
