Why we use "R", "r" in vector notations

In general when we want to define a vector to a point (Let's say from the origin of the coordinate system used)the letter we use to imply this vector will be "r" or "R".
It should have many reasons, but i think some of them are like this:
1 - It defines the "R"elation between two points. (The origin and the point defined)
2 - It implies the "R"esultant vector.

I will look for others...
If you have any idea please write.