Nonscientific, non material thought based on a belief in the existence of metaphysics rather than any one school of thought; restricted to or intended for an enlightened or initiated minority, because of abstruseness or obscurity.
Word Origin and History for esoteric:
1650s, from Greek esoterikos “belonging to an inner circle,” from esotero“more within,” comparative adverb of eso “within,” related to eis “into,” en“in”.
In English, originally of Pythagorean doctrines. According to Lucian, the division of teachings into exoteric and esoteric originated with Aristotle.