esoteric

Etymology

From Ancient Greek ἐσωτερικός (esōterikós, “belonging to an inner circle”), from ἐσωτέρω (esōtérō, “further inside”), comparative of ἔσω (ésō, “within”), from ἐς (es), εἰς (eis, “into”) (the term esoteric referred originally to the secret teachings of Greek philosophers, versus public or exoteric ones).

adj

1. Intended for or likely to be understood by only a small number of people with a specialized knowledge or interest, or an enlightened inner circle.
   The writing in this manual is very esoteric; I’d need a degree in engineering just to understand it!
2. Having to do with concepts that are highly theoretical and without obvious practical application; often with mystical or religious connotations.
3. Confidential; private.
   an esoteric purpose
   an esoteric meeting

noun

1. An esoteric doctrine or treatise; esoteric philosophy.
2. One who believes, or is an initiate, in esoteric doctrines or rites.