A foolish or stupid person; a blockhead.
From 'aglet' (the plastic or metal sheath at the end of a shoelace) + 'head'. The term mockingly refers to someone as having a head as small or useless as an aglet, suggesting emptiness or stupidity.
This insult from the 1500s-1600s reveals how Renaissance people made fun of each other—calling someone by the name of a tiny, pointless object was considered quite witty, and it shows how aglets were so common (even then!) that people used them as metaphors.
Complete word intelligence in one call. Free tier — 50 lookups/day.