n.1 being twofold; duality.
2 Philos. the theory that in any domain of reality there are two independent underlying principles, e.g. mind and matter, form and content (cf. IDEALISM, MATERIALISM).
3 Theol. a the theory that the forces of good and evil are equally balanced in the universe. b the theory of the dual (human and divine) personality of Christ.
Derivatives:
dualist n. dualistic adj. dualistically adv.