"Proof against" means something that is able to withstand or resist the effects of something else. Synonyms for this term include immune, impervious, insensitive, invulnerable, secure, shielded, fortified, guarded, resistant, and protected. These words describe something that is not vulnerable to external influences, and that is resistant to damage or harm. They can be used in a variety of settings, such as when discussing a new vaccine that provides immunity to a disease, or to describe a building that is fortified against natural disasters. No matter the context, synonyms for "proof against" all imply a level of resistance and protection that is vital for success in an unpredictable world.