es·o·ter·ic 
(ĕs′ə-tĕrĭk)
(ĕs′ə-tĕrĭk)adj.
1.
a. Intended for or understood by only a small group, especially one with specialized knowledge or interests: an esoteric philosophical doctrine. See Synonyms at mysterious.
b. Relating to or being a small group with specialized knowledge or interests: an esoteric circle.
2. Not known by or suitable for the public; private: Few understood the celebrity's esoteric side.
n.
1. One that is esoteric.
2. esoterics Esoteric matters; esoterica: "The course ... is anything but an exercise in ivory tower esoterics" (Sharon Waxman).
[Greek esōterikos, from esōterō, comparative of esō, within; see en in the Appendix of Indo-European roots.]
es′o·teri·cal·ly adv.