pinhead

noun

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…”

   “Settlements some centuries old, and still no bigger than pinheads on the untouched expanse of their background.”

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”

   “My daddy repairs cars driven by women who are pinheads.”

   “Percy, who hadn't noticed that Fred had bewitched his prefect badge so that it now read "Pinhead," kept asking them all what they were sniggering at.”

3. (slang)A telemark skier.
4. (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.”

   “Zip the What-Is-It was simply a Negro idiot. […] For half an hour at a time, David Belasco used to watch Zip at Coney Island. The producer insisted he saw signs of intelligence in the pinhead […]”

5. (slang)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.”

   “Crickets can be purchased in many sizes from newborns ("pinheads") to adults.”

6. The immature juvenile fruiting body of a mushroom prior to its gills opening.
7. (derogatory, slang)A member of the Provisional IRA.