<p><strong>Noun</strong></p><ul><li>Philosophy.</li><li>(In metaphysics) Any of various theories holding that there is only one basic substance or principle as the ground of reality, or that reality consists of a single element. Compare dualism, pluralism.</li><li>(In epistemology) A theory that the object and datum of cognition are identical. Compare pluralism.</li><li>The reduction of all processes, structures, concepts, etc., to a single governing principle; the theoretical explanation of everything in terms of one principle.</li><li>The conception that there is one causal factor in history; the notion of a single element as primary determinant of behavior, social action, or institutional relations.</li></ul>