[1] : The Collaborative International Dictionary of English v.0.48

chiasm \chi"asm\ kimac"a^z'm, chiasma \chias"ma\
   k-ia^z"m.a, n. nl. chiasma, fr. gr. chi`asma two
   lines placed crosswise, fr. ? to mark with a chi. anat.
   a commissure; an intersection or crossing of two tracts;
   especially, the optic commissure, or crucial union of the
   optic nerves. -- chias"mal, a..
   1913 webster chiasmatic
   chiasmal
see also:
chias"mal 

[2] : WordNet (r) 2.0

chiasm
     n : an intersection or crossing of two tracts in the form of the
         letter x syn: chiasma, decussation
see also:
chiasma decussation 

Chiasm >> C Words
Chiasm, definition of term: Chiasm
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