tetrad

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tetrad

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From Ancient Greek τετράς (tetrás), analysable as tetra- +‎ -ad.

• (Received Pronunciation, General American) IPA^(key): /ˈtɛtɹæd/

• Audio (Southern England):

  (file)

• Hyphenation: tet‧rad

tetrad (plural tetrads)

1. A group of four things.

   Synonyms: foursome, quartet; see also Thesaurus:quartet

   • 2010, Siddhartha Mukherjee, The Emperor of All Maladies, Fourth Estate (2011), page 177:

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

2. (biology) Two pairs of sister chromatids (a dyad pair) aligned in a certain way and often on the equatorial plane during the meiosis process.
3. (biology) A group of four haploid and immature pollen grains in tetrahedral fashion produced by meiotic microsporogenesis.
4. (cartography) A unit of land area of two by two (that is, four) square kilometres.
   • 2010, Richard Mabey, Weeds: How Vagabond Plants Gatecrashed Civilisation and Changed the Way We Think about Nature, London: Profile Books, →ISBN:

     They took figures for the abundance of invasive weeds mapped according to the normal grid unit of the 'hectad', or 10 × 10 km square, and then looked at how abundant these species were mapped at a much finer scale – in 'tetrads', or 2 × 2 km squares, inside these hectads.

5. (chemistry) A tetravalent atom or radical.
6. (mathematics) A group of four basis vectors for a four-dimensional manifold in differential geometry.
7. (music) A chord comprised of four notes; a tetrachord.

• (group) monad, duad/dyad, triad, tetrad, pentad, hexad, hebdomad/heptad, ogdoad/octad, ennead/nonad, decad/decade, hendecad, dodecad/duodecade, chiliad

• tetrad of Fallot
• tetradic

• ratted, tarted