The terminology question is confused by the fact that, in the US, "liberal" means "leftist", whereas in much (all?) of Europe or maybe even the rest of the world, "liberal" is more associated with classical liberalism, i.e. closer to what is called "libertarian" in the US (although I do feel that libertarianism is like classical liberalism taken to the extreme).

In any case, classical liberalism was only developed in the 19th century, while the usage of "left" and "right" is slightly older: it dates back to the French Revolution where it just happened that opposing factions would sit at opposite ends of the assembly. Given the chaotic nature of the French Revolution, what these opposite ends would represent would change countless times, but in general, the left wing was more associated with progressivism and the will of the Third Estate and the right wing was more conservative. Communism didn't even exist at the time, although arguably the first proto-communist advocate, Gracchus Babeuf, did emerge later in the French Revolution (he was offed by the "left wing" itself, though).