What does scatterbrain mean?

informal. : a person who is forgetful, disorganized, or unable to concentrate or think clearly The English, who had raised eccentricity and poor organization to a high art, and placed the scatterbrain on a pedestal, loathed such Middle European things as rules, conventions, and dictatorships.—

Is scatterbrain an adjective?

The adjective scatterbrained is perfect for describing someone who's disorganized, flighty, and maybe a little silly.