Arcane
Part of speech: adjective
Definition: Understood by only a few; obscure; requiring secret or mysterious knowledge.
Example sentence: Literary theory has become a parody of science, generating its own arcane jargon. In the process, tragically, it discourages love of literature for its own sake.
Esoteric
Part of speech: adjective
Definition: Understood only by a chosen few or an enlightened inner circle.Having to do with concepts that are highly theoretical and without obvious practical application.Confidential; private.
Example sentence: When I first started playing music in 1955, there was just a small body of people that knew it. It was a very esoteric type of thing.