Source : Webster's Revised Unabridged Dictionary (1913)

Sanctum \Sanc"tum\, n. [L., p. p. of sancire to consecrate.]
   A sacred place; hence, a place of retreat; a room reserved
   for personal use; as, an editor's sanctum.

   {Sanctum sanctorum} [L.], the Holy of Holies; the most holy
      place, as in the Jewish temple.

Source : WordNet®

sanctum sanctorum
     n 1: a place of inviolable privacy; "he withdrew to his sanctum
          sanctorum, where the children could never go" [syn: {sanctum}]
     2: (Judaism) sanctuary comprised of the innermost chamber of
        the Tabernacle in the temple of Solomon where the Ark of
        the Covenant was kept [syn: {holy of holies}]