Why is the ninth month called September?
1550s, from Medieval Latin algebra, from Arabic al jebr "reunion of broken parts," as in computation, used 9c. by Baghdad mathematician Abu Ja'far Muhammad ibn Musa al-Khwarizmi as the title of his famous treatise on equations ("Kitab al-Jabr w'al-Muqabala" "Rules of Reintegration and Reduction"), which also introduced Arabic numerals to the West. The accent shifted 17c. from second syllable to first. The word was used in English 15c.-16c. to mean "bone-setting," probably from Arab medical men in Spain.