pinhead

noun6

1. •
   The head of a pin. (Frequently used in size comparisons.)

   • The moment the nitre was red hot, the coal, previously reduced to small pieces of the size of a pinhead, was projected in portions of one or two grains at a time… — 1810
2. •
   (slang) A foolish or stupid person.

   • I don't want to be a pinhead no more / I just met a nurse that I could go for — 1977
3. •
   (slang) 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".

   • The microcephalic idiot is an unfortunate with a "pinhead," sometimes exhibited as a "what's-it" in circus side-shows, whose mental age never goes beyond that of an imbecile. — 1939
4. •
   A newborn cricket used as food for pets.

   • A newly hatched gecko will need pretty small crickets, but you will not have to go all the way down to pinheads. — 1994
5. •
   The immature juvenile fruiting body of a mushroom prior to its gills opening.
6. •
   (slang) A telemark skier.

noun1

1. •
   (slang, offensive) A member of the Provisional IRA.