tri·chot·o·my 
(trī-kŏtə-mē)
(trī-kŏtə-mē)n. pl. tri·chot·o·mies
1. Division into three parts or elements.
2. A system based on three parts or elements, especially the theological description of humans as consisting of body, soul, and spirit.
[New Latin trichotomia : Greek trikha, in three parts; see trei- in the Appendix of Indo-European roots + New Latin -tomia, -tomy.]
tri·choto·mous adj.
tri·choto·mous·ly adv.