From Greek 'esoterikos' (for the inner circle) — Aristotle's private teachings vs. public lectures. Opposite of 'exoteric.'
Intended for or likely to be understood by only a small number of people with a specialized knowledge or interest.
From Greek 'esōterikos' (ἐσωτερικός, belonging to an inner circle, inner), the comparative form of 'esō' (ἔσω, within, inward), from 'eis' (εἰς, into), from PIE *h₁en (in). Aristotle reportedly divided his teachings into 'exoteric' (ἐξωτερικός, for the outer circle, the public) and 'esoteric' (for the inner circle of advanced students). The opposite term 'exoteric' (from 'exō,' outside) is rarely used today, but the pair perfectly captures
The tradition holds that Aristotle taught two kinds of lessons: morning 'esoteric' lectures for his inner circle of advanced students (the 'peripatos,' or walking discussions), and afternoon 'exoteric' lectures open to the general public. Whether this is historically true is debated, but the pair of words stuck. 'Exotic' is a cousin — from Greek 'exōtikos' (foreign, from outside) — making