scat·​ter·​brain ˈska-tər-ˌbrān 

Synonyms of scatterbrain

informal

: a person who is forgetful, disorganized, or unable to concentrate or think clearlyThe 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.—Simon Winchester