king vs King of England

king and King of England both are nouns.

Word	Noun	Adjective	Verb	Adverb
king	Yes	No	No	No
King of England	Yes	No	No	No

As nouns, King of England is a hyponym of king; that is, King of England is a word with a more specific, narrower meaning than king:

Other hyponyms of king include King of Great Britain, King of France, King of the Germans.

king (noun)	King of England (noun)
(chess) the weakest but the most important piece	the sovereign ruler of England when male
one of the four playing cards in a deck bearing the picture of a king
a checker that has been moved to the opponent's first row where it is promoted to a piece that is free to move either forward or backward
a male sovereign; ruler of a kingdom
a very wealthy or powerful businessman
a male competitor who holds a preeminent position
the husband or widower of a queen
preeminence in a particular category or group or field