from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A group or set of four.
  • n. A tetravalent atom, radical, or element.
  • n. Biology A four-part structure that forms during the prophase of meiosis and consists of two homologous chromosomes, each composed of two sister chromatids.
  • n. Botany Biology A group of four cells, as of spores or pollen grains, formed by division of one mother cell.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A group of four things.
  • n. A tetravalent atom or radical.
  • n. Two pairs of sister chromatids (a dyad pair) aligned in a certain way and often on the equatorial plane during the meiosis process.
  • n. Group of four haploid and immature pollen grains in tetrahedral fashion produced by meiotic microsporogenesis.

from the GNU version of the Collaborative International Dictionary of English

  • n. The number four; a collection of four things; a quaternion.
  • n. A tetravalent or quadrivalent atom or radical.

from The Century Dictionary and Cyclopedia

  • n. In cytology, a group of four chromosomes formed by the division of a single chromosome; a quadripartite chromosome.
  • n. The number four; also, a collection of four things. Also quadrad.
  • n. In chem., an atom the equivalence of which is four, or an element one atom of which is equivalent, in saturating power, to four atoms of hydrogen.
  • n. In morphology, a quaternary unit of organization resulting from individuation or integration of an aggregate of triads. See triad, dyad.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. the cardinal number that is the sum of three and one


from The American Heritage® Dictionary of the English Language, 4th Edition

Greek tetras, tetrad-.


  • Religious movements and cults are often founded on a tetrad of elements: a prophet, a prophecy, a book, and a revelation.

    The Emperor of All Maladies

  • To create a tetrad, and discover insights into any human technology whatsoever, consider any artifact, and ponder these questions:

    Man and Media: The Chronology

  • Incidentally, Radix is actually the first book in a thematic “tetrad”.

    Reading Challenge #10 – Radix AA Attanasio « It Doesn't Have To Be Right…

  • The color palette is actually pretty consistent with typical color scheme design methods looks sort of like a color tetrad was made once they settled on the precise shade of yellow.

    Day 9: Taking a break

  • You can generate single monochromatic, complimentary, triad, tetrad, analogic and accented analogic colour palettes.

    Color Scheme Designer Is A Diverse Palette Creator | Lifehacker Australia

  • (I, Thou, objective world) to a tetrad, by a process of completion, as it were, to embrace the “godhead that lives in impenetrable silence”, the objective counterpart of the Ego, which had been suggested to him by his readings of Eckhart.

    Hermann Weyl

  • Beyond the 1980's: Space defense, laser weapons, and the strategic tetrad (Hudson Institute paper) by Barry Smernoff

    OpEdNews - Quicklink: Weather warfare

  • In the commencement of these it is very difficult to determine those which will come to a crisis after a long interval; for these beginnings are very similar, but one should pay attention from the first day, and observe further at every additional tetrad, and then one cannot miss seeing how the disease will terminate.

    The Book Of Prognostics

  • Adjust the triad, tetrad and analogic views to sample a range of complementary colors

    Instant Color Schemes - Freshblog

  • View color families with mono, contrast, triad, tetrad and analogic relationships

    Instant Color Schemes - Freshblog


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  • When Tetris fever first swept the nation, Nintendo referred to the blocks as "Tetrads." I personally like that better than "Tetriminoes," the term that's accepted today.

    March 4, 2019