1) Abstruse 2) Apprehended by a small group 3) Cabalistic 4) Cryptic 5) Dennis Miller-esque 6) Difficult to understand 7) Esoteric 8) Gotten by few 9) Hard to know 10) Hidden 11) Hidden a crane away 12) Incomprehensible 13) Inscrutable 14) Known by few 15) Known by only a few 16) Known only by insiders Found on https://www.crosswordclues.com/clue/arcane
Ar·cane' adjective [ Latin arcanus .] Hidden; secret. [ Obsolete] 'The arcane part of divine wisdom.' Berkeley. Found on http://www.encyclo.co.uk/webster/A/114
known or understood by very few; mysterious; secret; obscure; esoteric: She knew a lot about Sanskrit grammar and other arcane matters. Found on https://www.infoplease.com/dictionary/arcane