If something’s inviolate, it’s sacred and must be protected. If you make an inviolate promise to your sister to never reveal her secret superhero identity, it's one you must honor and take very seriously.
Inviolate comes from the Latin word inviolatus, made up of in-, meaning “not” and violare, meaning “violate.” So inviolate describes something so sacred or pure that it must not be violated. It can be used to describe fundamental principles or rights, such as the inviolate right of free speech, but it can also describe things that must be kept safe and pure. You might believe that the natural coastline outside your city should remain inviolate and not be developed.