Recondite
Definition: obscure; difficult to understand
It comes from a Latin word meaning “to conceal.”
When I read the definition, I thought to myself, “That sounds like ‘esoteric.'” Then I checked a synonym guide, and the first synonym suggested was “esoteric.”
Why I Looked It Up
From Spam: A Shadow History of the Internet:
Their sources include all the canonical texts and work in the public domain available on sites like Project Gutenberg, as well as more recondie materials.