monarch vs ruler

monarch and ruler both are nouns.

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

As nouns, ruler is a hypernym of monarch; that is, ruler is a word with a broader meaning than monarch:

Other hypernyms of monarch include chief of state, head of state, swayer.

monarch (noun)	ruler (noun)
large migratory American butterfly having deep orange wings with black and white markings; the larvae feed on milkweed	measuring stick consisting of a strip of wood or metal or plastic with a straight edge that is used for drawing straight lines and measuring lengths
a nation's ruler or head of state usually by hereditary right	a person who rules or commands