Merriam-Webster Collegiate Dictionary - unitarian

 noun  Etymology: New Latin unitarius, from Latin unitas unity  Date: 1687  1.  a. often capitalized one who believes that the deity exists only in one person  b. capitalized a member of a denomination that stresses individual freedom of belief, the free use of reason in religion, a united world community, and liberal social action  2. an advocate of unity or a unitary system  • ~ adjective, often capitalized  • ~ism noun, often capitalized