- the branch of metaphysics that studies the nature of existence or being as such.
- (loosely) metaphysics.
- philosophy the branch of metaphysics that deals with the nature of being
- logic the set of entities presupposed by a theory
n.“metaphysical science or study of being,” 1660s (Gideon Harvey), from Modern Latin ontologia (c.1600), from onto- + -logy.