a·pos·ta·sy 
(ə-pŏstə-sē)
(ə-pŏstə-sē)n. pl. a·pos·ta·sies
Abandonment of one's religious faith, a political party, one's principles, or a cause.
[Middle English apostasie, from Old French, from Late Latin apostasia, defection, from Late Greek apostasiā, from Greek apostasis, revolt, from aphistanai, aposta-, to revolt : apo-, apo- + histanai, to stand, place; see stā- in the Appendix of Indo-European roots.]