tetrad

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

[Greek tetras, tetrad-.]

A group of four similar or related entities, as (1) any element or radical having a valence, or combining power, of four; (2) a group of four chromosomal elements formed in the pachytene stage of the first meiotic prophase; (3) a square of cells produced by division into two planes of certain cocci (sarcina).

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Tetrad may refer to:

• Tetrad (chromosomal formation), a chromosomal formation in meiosis
• Tetrad (general relativity), a mathematical frame of reference in general relativity
• Tetrad (genetics), the four spores of a yeast
• Tetrad (Greek philosophy), the first number formed by the addition and multiplication of equals
• Tetrad (index notation), a concept in differential geometry
• Tetrad (music), a set of four notes
• Tetrad (unit of area), an area 2km x 2km square
• Tetromino, a shape composed of four squares
• Tetrad of media effects, a pedagogical tool

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