{ Chiasm (kīăz'm), Chiasma (k&iuptack_;ăzm&adot_;), } n. [NL. chiasma, fr. Gr. chiasma two lines placed crosswise, fr. &unr_; to mark with a χ.] (Anat.) A commissure; an intersection or crossing of two tracts; especially, the optic commissure, or crucial union of the optic nerves. -- Chiasmal (&unr_;), a..
[1913 Webster]