the GNU version of the Collaborative International Dictionary of English
n. A commissure; an intersection or crossing of two tracts; especially, the optic commissure, or crucial union of the optic nerves.
The Century Dictionary and Cyclopedia
n. In anatomy, a decussation or intersection; specifically, the decussation of the optic nerves which occurs in nearly all vertebrates. See second cut under brain.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. an intersection or crossing of two tracts in the form of the letter X
Word Usage
"The optic chiasm is deeper in the brain than the corpus callosum, so it is not cut by the operation."