Which language does the word 'algebra' come from?
It comes from 'al-jabr' in al-Khwarizmi's 9th-century book.
'Algebra' derives from the Arabic 'al-jabr', a term Merriam-Webster glosses as 'bonesetting' or 'restoration'. It was not about fractures: the sense is reuniting or completing, and the word was used for the technique of moving a subtracted term to the other side of an equation, which is closely related to completing the square in quadratic equations.
The term is tied to the Persian scholar Muhammad ibn Musa al-Khwarizmi, who worked in Baghdad in the early 9th century. His treatise on calculation 'by completion and balancing' (al-jabr wa'l-muqabala) gave systematic rules for solving linear and quadratic equations. The Library of Congress holds a copy of this work in its collections. The book was written in words and geometric reasoning rather than the symbolic notation used today.
Al-Khwarizmi's name has a second legacy: Latinized as 'Algoritmi', it is the source of the word 'algorithm'. Europe learned the material through Latin translations from the 12th century onward. Europeans did not invent algebra from nothing, but earlier mathematicians in Babylonia, Greece and India had solved comparable problems; al-Khwarizmi's contribution was a general, systematic treatment, which is why his book is credited with naming the subject. The English word arrived via medieval Latin and Spanish forms of the Arabic term, and its original 'bonesetter' sense survived for a time in Spanish.