In some cults or religions only the upper echelons are allowed to use a particular parlance, usually arcane, sometimes truly ancient and long since dead.
Spanish, French and Italian have fairly satisfactory adjectives for such a language, respectively "iniciático", "initiatique" and "iniziatico" (close relatives). German uses somewhat less efficiently the prefix "Initiations-".
The closest term I could find in English so far is "initiatory", whose definition though seems to diverge slightly from the meaning I'm looking for, allegedly referring to something leading to the initiation rather than something you achieve only once you become an Adept.
Can anyone suggest a better word?