[ kahy-az-muh ]
/ kaɪˈæz mə /

noun, plural chi·as·mas, chi·as·ma·ta [kahy-az-muh-tuh] /kaɪˈæz mə tə/.

Anatomy. a crossing or decussation, as that of the optic nerves at the base of the brain.
Cell Biology. a point of overlap of paired chromatids at which fusion and exchange of genetic material take place during prophase of meiosis.
Also chi·asm [kahy-az-uh m] /ˈkaɪ æz əm/.

Origin of chiasma

1830–40; < Greek: crosspiece of wood, cross-bandage, equivalent to chi chi1 + -asma noun suffix

Related forms

chi·as·mal, chi·as·mic, chi·as·mat·ic [kahy-az-mat-ik] /ˌkaɪ æzˈmæt ɪk/, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for chiasm


chiasm (ˈkaɪæzəm)

/ (kaɪˈæzmə) /

noun plural -mas, -mata (-mətə) or -asms

cytology the cross-shaped connection produced by the crossing over of pairing chromosomes during meiosis
anatomy the crossing over of two parts or structures, such as the fibres of the optic nerves in the brain

Derived Forms

chiasmal or chiasmic, adjective

Word Origin for chiasma

C19: from Greek khiasma wooden crosspiece, from khiazein to mark with an X, from khi chi 1
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

Medicine definitions for chiasm


[ kī-ăzmə ]

n. pl. chi•as•mas

A crossing or intersection of two tracts, as of nerves or ligaments.
The point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over.

Related forms

chi•asmal null null adj.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.