The body of doctrine held by the followers of Lelio Sozzini, or Socinus (1525 to 1562), a priest of Siena, Italy, and of his nephew, Fausto Sozzini (1539 to 1604), who carried his teaching to Poland where it first became important.
The outstanding feature of Socinianism is its denial of the Trinity.
It bases its teaching on the Bible "interpreted by reason," consequently it denies all mysteries which reason cannot comprehend.
Generally speaking Socinians denied the Virgin Birth, though the older Socinians taught that Christ was the Logos (John 1), and so to be adored.
They also denied the Redemption, holding that the Passion of Christ is a mere example to us and a pledge of our forgiveness.
Socinianism spread to various parts of Europe in its earlier years.
While it is much akin to modern Unitarianism, it is not organically its forerunner.
New Catholic Dictionary