Control R for Loop maybe because it forms a ring around the object?
Maybe, yes.
It's a good memory aid. (Although you'll likely be using it so often, that you won't need a memory aid for this shortcut...)
I always thought about it as Roop Cut, you know like how Japanese pronounce the L? Well it helped me anyways.Β
I was thinking R for "Rope", since it's like wrapping a rope around the model. I think it's easier to remember since it visually looks similar too.
I connect both shortcut keys and think of it as "Control Ring" because it make rings around the mesh.