Definition of "pinhead"

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, Thomas Thomson, A System of Chemistry, Vol. 4, Bell & Bradfute, page 602

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

1899 February, Joseph Conrad, “The Heart of Darkness”, in Blackwood’s Edinburgh Magazine, volume CLXV, number M, New York, N.Y.: The Leonard Scott Publishing Company, […], part I, page 203

I don't want to be a pinhead no more / I just met a nurse that I could go for

1977, “Pinhead”, in Leave Home, performed by Ramones

My daddy repairs cars driven by women who are pinheads.

1990, Kindergarten Cop

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.

1998, J. K. Rowling, Harry Potter and the Chamber of Secrets, page 212

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, Amram Scheinfeld, Morton David Schweitzer, You and Heredity, Frederick A. Stokes Co., page 155

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 […]

1943, Oliver Ramsay Pilat, Sodom by the Sea: An Affectionate History of Coney Island, Garden City Publishing, page 187

A newly hatched gecko will need pretty small crickets, but you will not have to go all the way down to pinheads.

1994, Raymond E. Hunziker, Leopard Geckos‎, Publisher, page 16

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

2000, Manny Rubio, Scorpions: Everything About Purchase, Care, Feeding, and Housing‎, Barron's Educational Series, page 70