empty-headed

flighty, scatterbrained

Synonyms: brainless, dizzy, featherbrained, frivolous, giddy, harebrained, ignorant, illiterate, inane, know-nothing, silly, skittish, stupid, uneducated, unschooled, untaught, vacant, vacuous

Antonyms: cognizant, intelligent, sensible, slick, smart