monarch vs milkweed butterfly

monarch and milkweed butterfly both are nouns.

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

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

monarch and milkweed 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, monarch butterfly.

monarch (noun)	milkweed 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