A realm 's a dominion of a monarch or other sovereign ruler. The Old French word reaume, modern French royaume, was the word first adopted in English; the fixed modern spelling doesn't appear until the beginning of the 17th century. The word supposedly derives from medieval Latin regalimen, from regalis, of or belonging to a rex, (king). "Realm"'s particularly used for those states whose name includes the word kingdom (for example, the United Kingdom), to avoid clumsy repetition of the word in… (More on Realm)