designed for, understood by, or restricted to a small group, esp of the specially initiated: compare exoteric
Theoretical linguistics is a rather esoteric subject — John Lyons
hard to understand
private or confidential
an esoteric purpose
esoterically adv
esotericism /-siz(ə)m/ noun
[via Latin from Greek esōterikos, from esōterō inner, ultimately from en in]