The origin of X as unknown (Majhool)

[ghorbati]

Remember reading it in an introduction to Khaarazmi's book of
Aljabro val Moghabelah...it claimed that X in old Spanish sounded
She and Khaarazmi's book in Muslim spain was a popular book
especially for accounting in royal courts. There is a word used in
Khaarazmi's book and that is Shey which means thing in Arabic.
That word was used for unknown...

I asked a Spanish friend of mine and he confirmed X could have
sounded "sh"... considering no other explanation, I think the above
was a sensible explanation...