- esoteric (adj.)
- 1650s, from Greek esoterikos "belonging to an inner circle" (Lucian), from esotero "more within," comparative adverb of eso "within," from PIE *ens-o-, suffixed form of *ens, extended form of root *en "in" (see en- (2)). Classically applied to certain popular and non-technical writings of Aristotle, later to doctrines of Pythagoras. In English, first of Pythagorean doctrines.
