What is the name of the symbol for the square root?

In mathematics, the radical sign (or radical symbol or root symbol or radix) is a symbol for the square root or higher-order root of a number.

The origin of the root symbol √ is largely speculative. Some sources imply that the symbol was first used by Arab mathematicians. One of those mathematicians was Abū al-Hasan ibn Alī al-Qalasādī (1421–1486). Legend has it that it was taken from the Arabic letter "ج‎" (ǧīm, which is the first letter in the Arabic word "جذر‎" (jadhir, meaning "root"). However, many scholars, including Leonhard Euler, believe it originates from the letter "r", the first letter of the Latin word "radix" (meaning "root"), referring to the same mathematical operation.

The symbol was first seen in print without the vinculum (the horizontal "bar" over the numbers inside the radical symbol) in the year 1525 in Die Coss by Christoff Rudolff, a German mathematician. In 1637 Descartes was the first to unite the German radical sign √ with the vinculum to create the radical symbol in common use today.