[arc] n [ME ark, fr. MF arc bow, fr. L arcus bow, arch, arc--more at arrow] (14c) 1: the apparent path described above and below the horizon by a celestial body (as the sun)
2: something arched or curved
3: a sustained luminous discharge of electricity across a gap in a circuit or between electrodes; also: arc 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 esp. in the phrase of arc "11 minutes 3 seconds of ~"
arc vi arced ; arc.ing (1893) 1: to form an electric arc
2: to follow an arc-shaped course "the missile ~ed across the sky" arc adj [arc sine arc or angle (corresponding to the) sine (of so many degrees)] (ca. 1949): inverse 2--used with the trigonometric functions and hyperbolic functions