Serbian language has a distinction between “smer” and “pravac”.
- “smer” is a straight line when you turn towards something. It's similar to a vector or a ray in maths. For example, “left”.
- “pravac” is a straight line that extends behind you. It's like a line in maths: there's no preferred way about which is “forward” and which is “backwards”. For example “left-right”.
We usually extends these meanings outside of “straight line”. For example, a train is going back-and-forth between towns A and B means that its “pravac” is A-B. In other words, it goes both from A to B and from B to A, but the line it follows is the same.
It doesn't mean just a “road”; it's specifically implying movements in both directions. For the same reason, it's not a “line”, although we do say “line” for buses for example -- which go back-and-forth between two destinations. But this feels more like a phrase “bus line”, and without a context “line” sounds just a regular straight line drawn with a pencil. “Way” also comes to mind, but this
How do I casually differentiate between these in English?
I head people using direction for both meanings, although with a heavy bias towards “smer” (when start and end points are different).
I don't know how to tag this. It doesn't necessarily have to be one word, nor am I looking for translation; I've used my native language as an example to describe the difference. This is similar, but asks specifically in mathematical context.