something arched or curved
a continuous portion of a curve, e.g. of a circle or an ellipse
the apparent path followed by a planet or other celestial body
a sustained luminous discharge of electricity across a gap in a circuit or between electrodes
= arc lamp
in mathematics, used to express the inverse of a trigonometric function as in arc sine (written arcsin or sin-1) and arc cosine (written arccos or cos-1)
[Middle English ark via Old French from Latin arcus bow, arch1, arc]