Agaricus arvensis vs horse mushroom

Agaricus arvensis and horse mushroom both are nouns.

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

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

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

Agaricus arvensis (noun)	horse mushroom (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