Definition of "Unitarian"

Unitarian

noun
plural Unitarians
1. (now inexact) Alternative letter-case form of unitarian: any Christian who denies the doctrine of the Trinity.
  Quotations
  But since Smith's ( of Norwich ) Bill passed , in 1813 , relieving Unitarians, as a religious sect, from the operation of the old law
  1836, Alexander Fleming, A Narrative of the Proceedings of the Presbytery of Paisley
2. A follower of Unitarian Universalism or a similar non-credal religion that originated historically from Christian Unitarianism.
  Quotations
  The Unitarians never kneel. But I want to kneel.
  2020, Jenny Offill, Weather, Granta Books (2021), page 197
3. (rare) Alternative letter-case form of unitarian: any monotheist, particularly non-Christian monotheists (Muslims, Jews, etc.) as discussed from a Christian perspective.
4. A member of a political movement advocating a unitary state rather than a federal one, especially the Unitarios of nineteenth century Argentina (known as the Unitarian Party in English).
adjective
comparative more Unitarian, superlative most Unitarian
1. Pertaining to Unitarianism.
  Quotations
  It was no less than whether the psychic movement in Britain was destined to take a Unitarian or a Trinitarian course.
  1925 July – 1926 May, A[rthur] Conan Doyle, “In which Traps are Laid for a Great Quarry”, in The Land of Mist (eBook no. 0601351h.html), Australia: Project Gutenberg Australia, published April 2019