Antipope

n. pope who is elected in opposition to a canonically chosen pope

An antipope is a person who makes a widely accepted claim to be the lawful Pope, in opposition to the Pope recognized by the Roman Catholic Church. Antipopes are typically those supported by a fairly significant faction of cardinals. Persons who claim to be the Pope but have few followers, such as the modern Sedevacantist antipopes, are not generally counted as antipopes, and therefore are ignored for regnal numbering.
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(n.)
One who is elected, or claims to be, pope in opposition to the pope canonically chosen; esp. applied to those popes who resided at Avignon during the Great Schism.
  

antipope /'æntipoup/
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