emperor vs monarch

emperor and monarch both are nouns.

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

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

Other hypernyms of emperor include crowned head, sovereign.

emperor (noun)	monarch (noun)
large richly colored butterfly	large migratory American butterfly having deep orange wings with black and white markings; the larvae feed on milkweed
large moth of temperate forests of Eurasia having heavily scaled transparent wings	a nation's ruler or head of state usually by hereditary right
red table grape of California
the male ruler of an empire