atrial vs atrium

atrial is not a noun while atrium is a noun.

Word	Noun	Adjective	Verb	Adverb
atrial	No	Yes	No	No
atrium	Yes	No	No	No

atrial (noun)	atrium (noun)
	the central area in a building; open to the sky
	any chamber that is connected to other chambers or passageways (especially one of the two upper chambers of the heart)

atrial (adjective)	atrium (adjective)
of or relating to a cavity or chamber in the body (especially one of the upper chambers of the heart)