horse mushroom vs Agaricus arvensis

horse mushroom and Agaricus arvensis both are nouns.

Word	Noun	Adjective	Verb	Adverb
horse mushroom	Yes	No	No	No
Agaricus arvensis	Yes	No	No	No

As nouns, horse mushroom and Agaricus arvensis are synonyms defined as:

horse mushroom and Agaricus arvensis: coarse edible mushroom with a hollow stem and a broad white cap

horse mushroom (noun)	Agaricus arvensis (noun)
coarse edible mushroom with a hollow stem and a broad white cap	coarse edible mushroom with a hollow stem and a broad white cap