Realm

The word supposedly derives from medieval Latin regalimen, from regalis, of or belonging to a rex 'king'.

[2] The word rex itself is derived from the Latin verb regere, which means 'to rule'.

Thus the literal meaning of the word realm is 'the territory of a ruler', traditionally a monarch (emperor, king, grand duke, prince, etc.).

It is also useful to describe those countries whose monarchs are called something other than "king" or "queen"; for example, the Grand Duchy of Luxembourg is a realm but not a kingdom, since its monarch holds the title Grand Duke rather than King.

The term may commonly be used to describe any of the "Commonwealth realms", which are kingdoms in their own right and share the same person as monarch, though they are fully independent of each other.