blank brainless dizzy empty empty-headed empty-minded empty-pated empty-skulled featherbrained featherheaded flighty fluttery frivolous gaga giddy giddy-brained giddy-headed giddy-pated giddy-witted harebrain harebrained hollow inane jejune rattleheaded rattlepated scatterbrained scramblebrained shatterbrained silly skittish thoughtless vacant vacuous vapid witless