pinhead

Short definition from Wiktionary

Noun

1. 1
   The head of a pin. (Frequently used in size comparisons.)
2. 2
   A foolish or stupid person.
3. 3
   A telemark skier.
4. 4
   A human head that is unusually tapered or small, often due to microcephaly, or a person with that trait. Often promoted in freak shows as "human pinheads".
5. 5
   A newborn cricket used as food for pets.
6. 6
   The immature juvenile fruiting body of a mushroom prior to its gills opening.
7. 7
   A member of the Provisional IRA.