Merriam-Webster Collegiate Dictionary - arc

 abbreviation  1. AIDS-related complex  2. American Red Cross ARC  I. noun  Etymology: Middle English ark, from Anglo-French ~ bow, from Latin ~us bow, ~h, ~ — more at arrow  Date: 14th century  1. the apparent path described above and below the horizon by a celestial body (as the sun)  2.  a. something ~hed or curved  b. a curved path the ~ of a fly ball  3. a sustained luminous discharge of electricity across a gap in a circuit or between electrodes; also ~ lamp  4. a continuous portion (as of a circle or ellipse) of a curved line  5. degree measurement on the circumference of a circle — used especially in the phrase of ~ 11 minutes 3 seconds of ~  6. a continuous progression or line of development a story's dramatic ~  II. intransitive verb  (~ed; ~ing)  Date: 1893  1. to form an electric ~  2. to follow an ~-shaped course  III. adjective  Etymology: ~ sine ~ or angle (corresponding to the) sine (of so many degrees)  Date: circa 1949 inverse 2 — used with the trigonometric functions and hyperbolic functions