Definition of "tetrad" [tet•rad]

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Religious movements and cults are often founded on a tetrad of elements: a prophet, a prophecy, a book, and a revelation."
• "To create a tetrad, and discover insights into any human technology whatsoever, consider any artifact, and ponder these questions:"
• "Incidentally, Radix is actually the first book in a thematic “tetrad”."