The Collaborative International Dictionary
Sabellianism \Sa*bel"li*an*ism\, n. (Eccl.) The doctrines or tenets of Sabellius. See Sabellian, n.
Wiktionary
n. (context Christianity English) A Christian belief which holds that God the Father and God the Son are one in the same, the latter often being termed Patripassianism in that it implies God the Father personally suffered on the Cross.
Wikipedia
In Christianity, Sabellianism in the Eastern church or Patripassianism in the Western church (also known as modalism, modalistic monarchianism, or modal monarchism) is the nontrinitarian or anti- trinitarian belief that the Heavenly Father, Resurrected Son, and Holy Spirit are three different modes or aspects of one monadic God, as perceived by the believer, rather than three distinct persons within the Godhead—that there are no real or substantial differences among the three, such that there is no substantial identity for the Spirit or the Son.
The term Sabellianism comes from Sabellius, who was a theologian and priest from the 3rd century.
Usage examples of "sabellianism".
One account of it says that the manuscript leans toward Sabellianism, and that it even approaches Pelagianism.