Source : Webster's Revised Unabridged Dictionary (1913)

Decussation \De`cus*sa"tion\, n. [L. decussatio.]
   Act of crossing at an acute angle, or state of being thus
   crossed; an intersection in the form of an X; as, the
   decussation of lines, nerves, etc.

Source : WordNet®

decussation
     n : an intersection or crossing of two tracts in the form of the
         letter X [syn: {chiasma}, {chiasm}]