clandestine, secret or furtive
The backstairs (stairs at the rear of a building).
Little known; esoteric, secret.
Difficult to grasp or understand; abstruse, profound.
Having mastery over one's field, including its esoteric minutiae; learned.
Deliberately employing abstruse or esoteric allusions or references; intentionally obscure.
A recondite (hidden or obscure) person or thing.
A scholar or other person who is recondite, that is, who has mastery over his or her field, including its esoteric minutiae.