a·pos·ta·sy (ə-pŏs'tə-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 Indo-European roots.]