Currently I’m reading Amin Maaluf’ Samarcande. He mentioned that Omar El Khayam used the word شيء or شي for his mathematical studies, this word was transformed into Chi, and later on to the famous X.
Check this out, from “the meanings of X“:“x commonly represents an unknown variable. Even though any letter can be used, x is the most common choice. This usage can be traced back to the Arabic word šay’ شيء = “thing”, which in translated algebra texts and similar was taken into Old Spanish with the pronunciation “šei”, which was written xei, which was soon habitually abbreviated to x. (Spanish pronunciation of “x” has changed since.) But some sources say that this x is an abbreviation of Latin causa which was a translation of Arabic شيء. That started the habit of using letters to represent quantities in algebra.”
I really like Omar El Khayyam 🙂 , and not just for his ruba3eyat, I like him for being a poet, a mathematician and astronomer, my three favorite subjects. In one of his ruba3eyat, he said that his utmost wish is to have his own observatory and a garden (tab3an along with a glass of wine and a pretty lover, bas ma 3aleina), in one way or another this is the ultimate thing a person can wish for,,,