A word for "1-dimensional variable"?

Question

Is there any noun or adjective (other than 1-manifold) that can reasonably be used for a variable that is constrained to a 1-dimensional space?

I would want the following examples to qualify:

1. A variable in $\mathbb{R}$
2. A variable modeling orientation within $\mathbb{R^2}$ (circular topology)

My first impulse was to use scalar but I'm not sure whether its meaning explicitly forbids the 2nd example above.