1) Abstruce matters 2) Abstruse facts or things 3) Abstruse matters 4) Arcanum 5) Crossword topics, often 6) Dark matter 7) Facts known to few 8) Recondite matters 9) Recondite matters or items 10) Secret 11) Things few understand 
[medication] Esoterica is an over-the-counter topical ointment applied to the skin for the purpose of lightening freckles, age spots, chloasma, melasma, and other skin discolorations due to a benign localized increase in the production of melanin. Esoterica may have other appropriate medical uses as determined by a physician. == Active and ...
[n] - secrets known only to an initiated minority
noun secrets known only to an initiated minority
things understood by or meant for a select few; recondite matters or items. · curiosa (def. 1).