Eleusinian

[el-yoo-sin-ee-uh n]

of or relating to Eleusis or to the Eleusinian mysteries.

a native or inhabitant of Eleusis.

Origin of Eleusinian

1635–45; < Latin Eleusini(us) < Greek Eleusínios of Eleusis + -an

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

So far so good; but this was only the first step of initiation into these Eleusinian mysteries.
St. Winifred's
Frederic W. Farrar
The Eleusinian temples had been erected in honour of the goddess Demeter.
Christianity As A Mystical Fact
Rudolf Steiner
Whence the prophetic Sybils, whence and what the Eleusinian mysteries?
Blackwood's Edinburgh Magazine, Vol. 65, No. 400, February, 1849
Various
Particularly characteristic of this is the legend of the Eleusinian mysteries.
Elements of Folk Psychology
Wilhelm Wundt
It was divided between the treasury of Zoroaster and that of the Eleusinian mysteries.
The Magic of the Middle Ages
Viktor Rydberg

Word Origin and History for eleusinian

adj.

1640s, "pertaining to Eleusis," town outside Athens, site of the mystery associated with the cult of Demeter, goddess of harvests, and her daughter.