The words of dismissal in the Eleusinian Mysteries. A correspondent in Notes and Queries says “knox” or “kogx” is the Sanscrit Canscha (the object of your desire); “ompax” is om (amen), pacsha (all is over). If this is correct, the words would mean, God bless you, Amen, The ceremonies are concluded. When a judge gave sentence by dropping his pebble into the urn of mercy or death, he said “Pacsha ” (I have done it). The noise made by the stone in falling was called pacsha (fate), and so was the dripping noise of the clepsydra, which limited the pleader's quota of time.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894