Source : Webster's Revised Unabridged Dictionary (1913)

Adytum \Ad"y*tum\, n. {Adyta}. [L., fr. Gr. ?, n., fr. ?, a.,
   not to be entered; 'a priv. + ? to enter.]
   The innermost sanctuary or shrine in ancient temples, whence
   oracles were given. Hence: A private chamber; a sanctum.