a person incapable of serious, connected thought.
careless, dizzy, empty-headed, flighty, forgetful, frivolous, giddy, harebrained, illogical, inattentive, irrational, irresponsible, madcap, silly, slaphappy, stupid, thoughtless, birdbrained
Origin of scatterbrain
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
exhibiting or characterized by lack of serious thought or concentration; disorganized; silly
a person who is incapable of serious thought or concentration
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
Online Etymology Dictionary, © 2010 Douglas Harper