Wordnet 3.0
NOUN (1)
1.
someone who is elected pope in opposition to another person who is held to be canonically elected;
- Example: "the antipopes resided in Avignon during the Great Schism"
The Collaborative International Dictionary of English v.0.48:
Antipope \An"ti*pope\, 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.
[1913 Webster]
WordNet (r) 3.0 (2006):
antipope
n 1: someone who is elected pope in opposition to another person
who is held to be canonically elected; "the antipopes
resided in Avignon during the Great Schism"