WordNet (r) 3.0 (2006):

esoterica
    n 1: secrets known only to an initiated minority

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "esoterica":
   abstruseness, arcanum, cabala, classified information, complexity,
   complication, confidence, confidential communication, crabbedness,
   crampedness, deepness, difficulty, enigma, guarded secret,
   hardness, hermetics, intricacy, knottiness, mystery,
   mystery of mysteries, personal matter, private matter,
   privileged communication, privity, profound secret, profoundness,
   profundity, reconditeness, restricted information, sealed book,
   secret, the occult