Definition of federal adjective in Oxford Advanced Learner's Dictionary. Meaning , pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. Federal is an adjective that describes a form of government or a country where power is divided between a central authority and regional units. It can also refer to a supporter of federation or the Union during the American Civil War. Learn the meaning of federal as an adjective, noun, and adverb in British and American English. Find out the synonyms, pronunciation, examples, and word origin of federal . Discover the meaning of federal , what federal means, and how to use federal correctly. Complete guide with definitions, examples, and usage tips.