A foolish or stupid person; an insult describing someone considered to lack intelligence or good sense.
Fool plus head (from Old English 'hēafod'). This folk insult compound emerged in Middle English, using the body-part metaphor to intensify the insult of foolishness.
Foolhead is a perfect example of how English folk insults work—by adding body parts to negative qualities (blockhead, knucklehead, bonehead), speakers made the insult more vivid and personal.
Complete word intelligence in one call. Free tier — 50 lookups/day.