monarch vs king

monarch and king both are nouns.

Word	Noun	Adjective	Verb	Adverb
monarch	Yes	No	No	No
king	Yes	No	No	No

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

monarch (noun)	king (noun)
large migratory American butterfly having deep orange wings with black and white markings; the larvae feed on milkweed	(chess) the weakest but the most important piece
a nation's ruler or head of state usually by hereditary right	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