adytum
The innermost sanctuary or shrine in a temple, from where oracles were given.
At the diſtance of about forty ſtadia from this temple of Æſculapius, there is an incloſure; and in it there is an adytum ſacred to Iſis. This is the moſt holy of every thing which the Greeks conſecrate to this goddeſs. For the Tithoreans neither think it proper to take up their reſidence there, nor to ſuffer any to enter the adytum, except ſuch as the goddeſs Iſis informs them by a dream ſhe thinks proper to admit.
A private chamber; a sanctum.
Although it was the custom for the priestesses to affect a holy fury, a species of temporary insanity, in the delivering of their oracles, yet it was also the custom to write them on the leaves of trees, and to deposit them at the entrances of their caves, or the adyta of their temples; and it was the object of the devotee to secure them before they were dispersed by the winds; […]
Where it comes from
Borrowed from Latin adytum, from Ancient Greek ἄδυτον (áduton, “innermost sanctuary; shrine”), inflected form of ἄδυτος (ádutos, “not to be entered”).
Adapted from the Wiktionary entry adytum (CC BY-SA 4.0).