ad·y·tum /ˈædɪtəm/

–noun, plural -ta  /-tə/
1. (in ancient worship) a sacred place that the public was forbidden to enter; an inner shrine.
2. the most sacred or reserved part of any place of worship.

1665–75; < L < Gk ádyton (place) not to be entered, equiv. to a– a-6 + –dyton, neut. of –dytos, verbid of dýein to enter


The group marched up warn marble, through an enormous arched portal, into an echoing hall, distinguished only by the high dome and an adytum or altar at the far end.

Source: Tales of the Dying Earth by Jack Vance.