Abstruse

abstruse \ab-STROOS; uhb-\, adjective:
Difficult to comprehend or understand.

One should be particularly suspicious when abstruse mathematical concepts (like the axiom of choice in set theory) that are used rarely, if at all, in physics -- and certainly never in chemistry or biology -- miraculously become relevant in the humanities or the social sciences.
-- Alan Sokal and Jean Bricmont, Fashionable Nonsense