軌

It is a phono-semantic compound, consisting of:

車 (cha/거, “cart, vehicle”) as the semantic element;

九 (gu, “nine”) as the phonetic element.

There is a hypothesis that 軌 was borrowed from the Tocharian word kursär/kwarsär, which is cognate with the Proto-Indo-European root ḱers- (“to run, move”), distantly related to English course (and many other ḱers- derivatives).

Common in technical/scientific vocabulary (astronomy, engineering).

Strongly associated with trajectory, orbit, and traces left behind.

Common compounds:

궤도 (軌道) – orbit, track, trajectory;

궤적 (軌跡) – track, trace, trajectory;

궤범 (軌範) – norm, model, rule;

철궤 (鐵軌) – railroad track (lit. “iron track”);