isoteric
/ɛsɪˈɒstɪrɪk/Definitions
1. adjective
Difficult to understand; requiring specialized knowledge.
“The professor’s esoteric lecture on quantum physics confused many students.”
2. noun
A subject or interest that is not widely understood or known, especially one that is considered obscure or abstruse.
“The club’s focus on esoterica drew a small but dedicated crowd.”