A tetrad is a group of four things. If you've ordered four pizzas for dinner, you can announce that you are serving a tetrad of pizzas.

You can use the noun tetrad to talk about a set of four numbers in math, or a group of four things in various branches of science — one kind of tetrad is a group of four spores in one specific type of yeast. It's more common in non-scientific speech to say quartet or quadruplet. Tetrad comes from a Greek root, the word tetras, "group of four," from tetra, or "four."

Definitions of tetrad
  1. noun
    the cardinal number that is the sum of three and one
    synonyms: 4, IV, Little Joe, four, foursome, quadruplet, quartet, quatern, quaternary, quaternion, quaternity
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    type of:
    digit, figure
    one of the elements that collectively form a system of numeration
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