'Superbious', and its alternate form, 'superbous', is an odd swirl in the English language. It comes to us from the Latin 'superbus', meaning proud or supercilious. From the early 1500s to the early 1700s 'superbious' was used in both the positive sense of someone fine or rightly proud, and the negative sense of someone who was arrogant. However, it was during this same time that the word 'superb', from the same root, came into use. Obviously, 'superb' eventually became much more common than 'superbious'.
If English was a constructed language, we would have the root 'super-', the noun 'superness', and the adjective 'superous'. Obviously, we did not go this route, and 'superb' won out as the the adjectival form. However, the attempt to coin 'superbious', containing the proper '-ous' suffix, makes perhaps a bit more sense than the rather odd 'superb'.
While the word 'superbious' (pronounced soopeerbis; IPA: /suˈper.bis/) is pretty well extinct these days, it does have a benefit over 'superb' in that it can be used in both the positive and the negative sense, which is not something generally done with 'superb'. It is becoming more common to use the Latin 'superbus' (pronounced soopeerboos; IPA: /suˈper.bus/) instead of 'superbious', as legal language and the famous king Lucius Tarquinius Superbus keep the Latin term in print. (It is worth noting that Tarquin also gave rise to the equally obscure adjective Tarquinish).