numskull or numbskull /numˈskul/ (informal)

A blockhead

numˈskulled adjective

• unsounder
• unsoundest
• unsoundly
• unsoundness
• unsoundnesses
• unsourced
• unsoured
• unsown
• unspar
• unspared
• unsparing
• unsparingly
• unsparingness
• unsparingnesses
• unsparred
• unsparring
• unspars
• unspeak
• unspeakable
• unspeakableness
• unspeakablenesses
• unspeakably
• unspeaking
• unspeaks
• unspecialised