Synonyms and related words :
brainless, crownless, foolish, ignorant, inept, insensate, irrational, lackbrained, lean-minded, lean-witted, mindless, not bright, of little brain, pea-brained, pin-brained, reasonless, senseless, slackminded, slackwitted, topless, ungifted, unintellectual, unintelligent, unreasoning, untalented, unthinking, unwise, witless