1. Someone who exercises supreme, permanent authority; especially, in a nation or other governmental unit, as: (a) A king, queen, or other noble person who serves as chief of state; a ruler or monarch; (b) A national governing council or committee.
2. A nation that governs territory outside its borders.
3. A gold coin formerly used in Great Britain.
4. Etymology: from about 1280, from Old French soverain, from Vulgar Latin superanus, "chief, principal"; which came from Latin super, "over".

The spelling of the English word sovereign (with g) is believed to be a result of the influence of reign, with which the word sovereign was associated according to folk etymology.