Square root
It is not really known where the square root symbol  comes from, but some people believe that it was from the letter r, which is the first letter of the Latin word radix (used in many languages). Radix means the root or base. Thus, radix quadratum from Latin refers most likely to the base of a square. Since the sides of a square are all equal, the word radix may be interpreted as side of a square—without actually so.