sovereign vs head of state

sovereign and head of state both are nouns.

Word	Noun	Adjective	Verb	Adverb
sovereign	Yes	Yes	No	No
head of state	Yes	No	No	No

As nouns, head of state is a hypernym of sovereign; that is, head of state is a word with a broader meaning than sovereign:

sovereign: a nation's ruler or head of state usually by hereditary right
head of state: the chief public representative of a country who may also be the head of government

Other hypernyms of sovereign include chief of state, ruler, swayer.

sovereign (noun)	head of state (noun)
a nation's ruler or head of state usually by hereditary right	the chief public representative of a country who may also be the head of government

sovereign (adjective)	head of state (adjective)
greatest in status or authority or power
(of political bodies) not controlled by outside forces