The head of a pin. Frequently used in size comparisons.
1810, Thomas Thomson, A System of Chemistry, Vol. 4, Bell & Bradfute, page 602: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…
1998, J. K. Rowling, Harry Potter and the Chamber of Secrets, page 212: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.
(slang, medicine) A human head that is unusually tapered or small, often due to microcephaly, or a person with that trait. Often promoted in Freak show as "human pinheads".
1939, Amram Scheinfeld and Morton David Schweitzer, You and Heredity, Frederick A. Stokes Co., page 155: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.
1943, Oliver Ramsay Pilat, Sodom by the Sea: An Affectionate History of Coney Island, Garden City Publishing, page 187:Zip the Pinhead 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 ...
1994, Raymond E. Hunziker, Leopard Geckos, Publisher, ISBN 079380258X, page 16:A newly hatched gecko will need pretty small crickets, but you will not have to go all the way down to pinheads.
2000, Manny Rubio, Scorpions: Everything About Purchase, Care, Feeding, and Housing, Barron's Educational Series, ISBN 0764112244, page 70:Crickets can be purchased in many sizes from newborns ("pinheads") to adults.
