es⋅o⋅ter⋅ic [ es uh tair ik, es oh tair ik]
1. understood by or meant for only the select few who have special knowledge or interest; recondite: poetry full of esoteric allusions.
2. belonging to the select few.
3. private; secret; confidential.
4. (of a philosophical doctrine or the like) intended to be revealed only to the initiates of a group: the esoteric doctrines of Pythagoras.
1645–55; < Gk esōterikós inner, equiv. to ester(os) inner + -ikos -ic
[L]et's not forget that many of the artists who are now "popular" -- Monet, Renoir, Picasso, even sometimes Old Masters like Titian and Rembrandt -- could be seen as absurdly difficult and esoteric to their contemporaries.
--Blake Gopnik, interviewed on Washingtonpost.com