Arc

1. n. The apparent arc described, above or below the horizon, by the sun or other celestial body. The diurnal arc is described during the daytime, the nocturnal arc during the night.
2. n. A portion of a curved line; as, the arc of a circle or of an ellipse.
3. n. A curvature in the shape of a circular arc or an arch; as, the colored arc (the rainbow); the arc of Hadley’s quadrant.
4. n. An arch.

The word meanings were obtained from OPTED(The Online Plain Text English Dictionary), which is based on “The Project Gutenberg Etext of Webster’s Unabridged Dictionary” which is in turn based on the 1913 US Webster’s Unabridged Dictionary (See Project Gutenburg), as a text file.