There is this one interesting post found here that says the following:
It says the ritual goes back to the earliest Zensunni, and stems from
event called "Siayla" meaning "the Light of truth" they gathered and
discussed the progress toward the religious goals of the year.
Considering that the Zensunni are a mixture between zen buddhism and sunni islam,
siayla sounds more arabic to me. Also, on the Wikipedia page for the Dune religions, there is this part:
Terminology of the Imperium also defines several Zensunni terms:
AULIYA: In the Zensunni Wanderers' religion, the female at the left
hand of God; God's handmaiden.(...)
These concepts are all more or less identifiable with Islamic
concepts: Auliya (Arabic: أولياء) is the Arabic word for saints
Auliya sounds very much like Siayla to me so I guess it's very likely to be an arabic term.