1911 Encyclopædia Britannica/Esoteric

ESOTERIC, having an inner or secret meaning. This term, and its correlative “exoteric,” were first applied in the ancient Greek mysteries to those who were initiated (ἔσω, within) and to those who were not (ἔξω, outside), respectively. It was then transferred to a supposed distinction drawn by certain philosophers between the teaching given to the whole circle of their pupils and that containing a higher and secret philosophy which was reserved for a select number of specially advanced or privileged disciples. This distinction was ascribed by Lucian (Vit. Auct. 26) to Aristotle (q.v.), who, however, uses ἐξωτερικοὶ λόγοι (Nic. Ethics) merely of “popular treatises.” It was probably adopted by the Pythagoreans and was also attributed to Plato. In the sense of mystic it is used of a secret doctrine of theosophy, supposed to have been traditional among certain disciples of Buddhism.