in the unit circle, names of the various points depending on the angle at the origin

Question

I found this image on German wikipedia, naming points related to the unit circle with letters.

Most makes sense, like S for Sine, C for Cosine, O for Origin, P for Point, T for Tangent, and K for Cotangent (in German it is Kotangens, and C is taken by Cosine anyways). Now what's still open is what D and E and b stand for. Does someone have an idea? Thanks a lot!

Background: I find it useful to have consistent naming for such things. It allows for briefer and more comprehensible descriptions. I find it of particular use when I program shaders.

Answer 1

They are just $(1,0)$ and $(0,1)$ and are not really that significant, so you don't really need to worry about them. I am not sure about what $D$ and $E$ stand for - it might be something in German (and my German is not very good to say the least). As @aschepler suggested, it might just be some available letters that mean nothing. As for $b$, it is the arc with angle $POD$

Answer 2

The $b$ stands for the German word for arc, which is $der~ Bogen$.

It is not clear to me why the letters $D$ and $E$ were chosen for the points $(1, 0)$ and $(0, 1)$, respectively. They could just be labels chosen since they are different from the other letters in the diagram.