one who denies the doctrine of the Trinity, believing that God exists only in one person [n -S]
person who maintains that God is one being, rejecting the doctrine of the Trinity
member of a liberal religious denomination founded upon the doctrine that God is one being, and giving each congregation complete control over its affairs
advocate of unity or centralization, as in government
pertaining to the Unitarians or their doctrines; accepting Unitarianism; belonging to the Unitarians