n (astronomy) That part of a circle which a heavenly body appears to pass through as it moves above and below the horizon. (defdate|from 14th c.)
n (geometry) A continuous part of the circumference of a circle (circular arc) or of an other curve. (defdate|from 16th c.)
n (context|electrics) A flow of current across an insulating medium; especially a hot, luminous discharge between either two electrodes or as lightning. (defdate|from 19th c.)