APOS'TASY, n.  [Gr. a defection, to depart.] 1.  An abandonment of what one has professed; a total desertion, or departure from one's faith or religion.2.  The desertion from a party to which one has adhered.3.  Among physicians, the throwing off of exfoliated or fractured bone, or the various solution of disease.4.  An abscess. 
 
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