I've seen schlicht-function for functions $f(x)=x +a x^2 + b x^3 + ...$$f(x)=x +a x^2 + b x^3 + \cdots$ for powerseries without constant term and $f'(0)=1 $. But I do not really know, whether this is really the german word schlicht (=simple) or only some coincidence.