rattlebrained (adj.)

• blank
• brainless
• dizzy
• empty
• empty-headed
• featherbrained
• flighty
• frivolous
• gaga
• giddy
• harebrained
• hollow
• inane
• jejune
• rattlepated
• scatterbrained
• silly
• skittish
• thoughtless
• vacant
• vacuous
• vapid
• witless