1. Used in biological contexts to describe a crossing. (In Latin anatomical terms the form decussatio is used, e.g. decussatio pyramidum). In anatomy the term chiasma or chiasm means much the same as decussation. (wikipedia.org)
2. A crossing or intersection of lines etc. so as to form an X-shape. (wiktionary.org)
Syn: Chiasma, chiasm
Word origin: Latin decussatus, crossed like the letter X.