Unitarian

n. [Fr. unitairien, It. unitario, N. Lat. unitarius, from Lat. unitas, unity.] 1. One who denies the doctrine of the Trinity, believing that God exists only in one person. 2. One opposed to dualism, in philosophy, science, and the like. 3. A monotheist. [Rare.] Fleming.

a. 1. Of, or pertaining to, Unitarians, or to their doctrines. 2. Of, or pertaining to, a system of philosophy, science, and the like, which is opposed to dualism. Sir W. Hamilton.