In the 9th century, Arab writers usually called one of the equal factors of a number jadhr (“root”), and their medieval European translator used the Latin word radix (from which derives the adjective radical). Radix is the Latin for root, and radical is the name of the square root symbol.
It is called a square root because you are having to find a number that is multiplied by itself to get the number that is intended. Let's you have to find the square root of 16. It would of course be 4 because 4*4 is 16. So in this case it could also be written as 4 to the second power. Hope this helped. :)
