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.

  • When you say that 'pravac is a straight line behind you' does that mean that it is only behind you, that is that it is not projected in front of you as well? Also, if I arrive from somewhere along my pravac (eg I have walked directly from the clock tower so the clock tower is on my pravac) but I then turn through 90 degrees does my pravac then not include the clock tower? Finally is my pravac of infinite length or does it extend only as far as the place I started from (eg the clock tower)?
    – BoldBen
    Apr 2, 2019 at 9:43
  • I said "that extends behind you", so it includes both front and back. I feel like you're too strict and formal with the definitions. Whether you can turn 90deg or not depends on the implicit context. In maths, smer is a vector/ray and pravac is a line. In context of roads, it doesn't necessarily have to be a strictly straight line; a bus which circulates around the town doesn't have a pravac, only smer (which is clockwise of counterclockwise). It usually does extend beyond. If cities A, B, C are collinear, in that order, you can say that you reach C by walking "in pravac of A-B". Apr 2, 2019 at 11:26
  • It's amazing how difficult it is for me explain this and how often people come up with more and more technical question about whether this-or-that counts as smer/pravac. This is the prime example of a language barrier for me. Apr 2, 2019 at 11:27
  • Hi Lazar, the reason I didn't know that pravac stretches out both in front and behind is that the phrase 'extends in a certain direction', in English means 'stretches out in that direction'. It is not the same as extending a line in geometry. Had you said 'extends in front and behind you' I would have understood the concept.
    – BoldBen
    Apr 3, 2019 at 17:06
  • Ah, now that I read it again I understand the confusion. Sorry if I sounded rude, was removing a lot of noise in the comment to fit the character count, which made it all look more stiff. Apr 3, 2019 at 17:12

1 Answer 1


What a coincidence! I had a very similar problem recently in trying to explain to someone how a polaroid (polarising filter) works. Its molecules are arranged parallel to each other and will stop the propagation of light having an E vector pointing one way along the molecules or in the opposite direction along the molecules. I wanted to say that it stops light with its E vector pointing in the same direction as the molecules, but that's not quite right, as we both understand.

The word I needed is 'alignment'. The polaroid stops light whose E vector has the same alignment as the molecules.

That solved my problem, but it's hardly casual or informal usage, and it won't be applicable in every case when you want to distinguish between a road aligned (say North–South) and a particular direction along that road. Not as versatile as smer and pravac.

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