Mysterium Magnum

Mysterium Magnum is Latin for "great mystery" and has several different associations and usages.

Paracelsus
Paracelsus and other alchemists employed the term "Mysterium Magnum" to denote primordial undifferentiated matter, from which all the Classical Elements sprang, sometimes compared with Brahman, aether and akasha.

Jakob Böhme
Jakob Böhme (1575–November 17, 1624) a German Christian mystic wrote a treatise entitled The Mysterium Magnum (1623).

Sacrament
"Mysterium Magnum" is often employed in Christian theology as a euphemism for "sacrament".