Abstruse
Part of speech: adjective
Definition: remote from apprehension; difficult to comprehend or understand; recondite; as in abstruse learning. concealed or hidden out of the way.
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: I thought of the idea of Summly in March or April 2011. I was 15 years old and I was revising for some kind of history exam. The problem was I was trying to find information that was useful to me. When you type into Google an esoteric term, you get quite a lot of stuff that's not relevant.