monarch vs monarch butterfly

monarch and monarch butterfly both are nouns.

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

As nouns, monarch and monarch butterfly are synonyms defined as:

monarch and monarch butterfly: large migratory American butterfly having deep orange wings with black and white markings; the larvae feed on milkweed

Other synonyms of monarch include Danaus plexippus, milkweed butterfly.

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