Which mathematician-astronomer of the House of Wisdom gave us the word algebra?

Al-Khwarizmi worked in Baghdad in the first half of the ninth century, under the caliph al-Ma'mun, and two ordinary English words come from him. His book on solving equations was titled, in part, al-jabr wa'l-muqabala - restoration and balancing, meaning the moves you make to get an equation into a solvable shape. Al-jabr became algebra. His own name, Latinised as Algoritmi, became algorithm.

The book itself looks strange to a modern eye because there is not a single symbol in it. Everything is words: a square and ten roots equal thirty-nine dirhams. He works through every type of quadratic systematically, gives a method for each, and then proves each method with a geometric construction. What he supplied was not a new trick but the idea that these problems form a small number of classes and each class has a procedure - which is what makes it algebra rather than a collection of puzzles.

His other work travelled just as far. He wrote the treatise on Hindu-Arabic numerals whose Latin translation is how Europe eventually acquired the decimal system and the zero, and he revised Ptolemy with corrected coordinates for several hundred places. The Latin form of his name, Algoritmi, became the word algorithm.