[ te-trad ]
/ ˈtɛ træd /


a group of four.
the number four.
Cell Biology. a group of four chromatids formed by synapsis at the beginning of meiosis.
Chemistry. a tetravalent or quadrivalent element, atom, or group.



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Origin of tetrad

1645–55; <Greek tetrad- (stem of tetrás) group of four
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Example sentences from the Web for tetrad

British Dictionary definitions for tetrad

/ (ˈtɛtræd) /


a group or series of four
the number four
botany a group of four cells formed by meiosis from one diploid cell
genetics a four-stranded structure, formed during the pachytene stage of meiosis, consisting of paired homologous chromosomes that have each divided into two chromatids
chem an element, atom, group, or ion with a valency of four
ecology a square of 2 × 2 km used in distribution mapping

Word Origin for tetrad

C17: from Greek tetras, from tettares four
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for tetrad

[ tĕtrăd′ ]


A group or set of four.
A tetravalent atom, radical, or element.
A group of four chromatids formed from each of a pair of homologous chromosomes that split longitudinally during the prophase of meiosis.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Scientific definitions for tetrad

[ tĕtrăd′ ]

A four-part structure that forms during prophase I of meiosis and consists of two homologous chromosomes, each composed of two identical chromatids. During prophase I of meiosis, one chromosome exchanges corresponding segments of genetic material with the other chromosome in the tetrad in the process called crossing over. See more at meiosis.
A group of four cells, as of spores or pollen grains, formed from a parent cell by meiosis. As part of the process of spermatogenesis, a spermatocyte divides into a tetrad of four spermatids, cells which go on to develop into sperm. See more at spermatogenesis.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.