noun

1. the branch of philosophy that deals with first principles and seeks to explain the nature of being or reality (ontology) and of the origin and structure of the universe (cosmology): it is closely associated with the study of the nature of knowledge (epistemology)
2. speculative philosophy in general
3. esoteric, often mystical or theosophical, lore
4. the theory or principles (of some branch of knowledge)
5. popularly any very subtle or difficult reasoning

Etymology: < ML metaphysica, neut. pl. < Gr (ta) meta (ta) physika, lit., (that) after (the) physics (in reference to location after the Physics in early collections of Aristotle's works)