D defs.my
Entry 1 sense Webster, 1913

Chiasm

/(kī"ăz'm)/ · Chi·asm · IPA /ˈkaɪ.æzəm/
01 n. A commissure; an intersection or crossing of two tracts; especially, the optic commissure, or crucial union of the optic nerves.
  1. 1.
    A commissure; an intersection or crossing of two tracts; especially, the optic commissure, or crucial union of the optic nerves.(Anat.)