algebra (n.)
1550s, from Medieval Latin algebra, from Arabic al jabr ("in vulgar pronunciation, al-jebr" [Klein]) "reunion of broken parts," as in reducing fractions to integers in computation, used 9c. by Baghdad mathematician Abu Ja'far Muhammad ibn Musa al-Khwarizmi as the title of his famous treatise on equations ("al-mukhtasar fi hisab al-jabr wa al-muqabala" "the compendium on calculation by restoring and balancing"), which also introduced Arabic numerals to the West. From Arabic jabara "reintegrate, reunite, consolidate." John Dee (16c.) calls it algiebar and almachabel. The accent shifted 17c. from second syllable to first.

The same word was used in English 15c.-16c. to mean "bone-setting," as was Medieval Latin algebra, probably from Arab medical men in Spain.