MONARCHIANISM. – The name formerly given to the heresy of modalism or Sabellianism, and also, by some modern and less properly, to that of adoptionism, because, in an effort to safeguard monotheism, the first denied the real distinction of the Divine Persons in the Trinity, while the second denied the divinity of Christ, thus interpreting in an heretical manner the ancient monotheistic saying that in the faith in divinity the monarchy must be upheld. V. ADOPTIONISM; MODALISM.
Enciclopedia Cattolica