pin-head

/P IH1 N EH0 D/
noun
  1. 1

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

  2. 2

    An ignorant, naive, 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

    (pet stores) A newborn cricket used as food for pets.

  6. 6

    (mycoculture) The immature juvenile fruiting body of a mushroom prior to its gills opening.

Source: https://en.wiktionary.org/wiki/pin-head, https://en.wiktionary.org/wiki/pinhead