animalcule

Etymology

Learned borrowing from Late Latin animalculum (“lowly or small animal”) + English -cule (diminutive suffix). Animalculum is derived from Latin animal (“animal; living creature”) + -culum (diminutive suffix); and animal from animāle, the nominative neuter singular of animālis (“animate, living; relating to living creatures”), from anima (“breath; life; soul, spirit”) (ultimately from Proto-Indo-European *h₂enh₁- (“to breathe”)) + -ālis (suffix forming adjectives of relationship). The English word is analysable as animal + -cule.

noun

1. (physiology, historical) A sperm cell or spermatozoon; also, the embryo that was formerly thought to be contained inside a spermatozoon in a fully developed state.
   [Antonie van] Leeuwenhoek's most mysterious finding was yet to come, however. Inside the animalcules in the thickest part of the semen he saw / all manner of great and small vessels, so various and so numerous that I do not doubt that they be nerves, arteries and veins. … 2001, David M. Friedman, “The Gear Shift”, in A Mind of Its Own: A Cultural History of the Penis, New York, N.Y.: The Free Press, page 76
2. (zoology, archaic) A microscopic aquatic animal, including protozoa and rotifers.
   If we are part of nature, then we are synonymous with it at the metaphysical level, every bit as much as the first all-but-inorganic animalcules that ever formed a chain of themselves in the blow hole of a primordial sea vent. 2011, John Jeremiah Sullivan, “La·hwi·ne·ski: Career of an Eccentric Naturalist”, in Pulphead, New York, N.Y.: Farrar, Straus and Giroux, →OCLC, pages 212–213
3. (obsolete) A small animal.