sovereign

As nouns the difference between sovereign and octroi

is that sovereign is a monarch; the ruler of a country while octroi is (historical) a privilege granted by the sovereign authority, such as the exclusive right of trade granted to a guild or society; a concession.

As an adjective sovereign

is exercising power of rule.

As nouns the difference between sovereign and royalism

is that sovereign is a monarch; the ruler of a country while royalism is impassioned allegiance to or advocacy of the establishment, maintenance, and/or interests of a particular king, royal house, or kingly dynasty; sometimes extended to the same of a non-royal (ie, grand ducal, imperial, or other) family or sovereign; often contrasted with monarchism.

As an adjective sovereign

is exercising power of rule.