There are many authoritative resources. Pick a dictionary or thesaurus or a grammar guide from the <i>version</i> of English you want to learn and use that as your reference.<p>When I say a version of English I mean British English or American English or Canadian English or Australian English or some other version of English. They all have differences in spelling (colour vs color etc) and differences in phrases and idioms.<p>English is so varied because it has travelled all over the world and changed in so many ways as a result - hence the forementioned varieties of English. For better or worse, it has become the international language of science, technology, business, and entertainment. In our internet age, that means it changes even more rapidly than other languages that don&#x27;t have such global reach.