Definition of pumpkin-head in US English:

pumpkin-head

noun

US
informal
  • A person with a head compared to a pumpkin; a fool, a dolt. Also: a head resembling or made from a pumpkin; specifically (a) a large or round head; (b) a head having the hair cut short all round.

Origin

Mid 18th century; earliest use found in William Kenrick (d. 1779), writer and translator. From pumpkin + head.

Pronunciation

pumpkin-head

/ˈpʌm(p)kɪn ˌhɛd/