late 14c., originally in reference to the sun's apparent motion in the sky, from Old French arc "bow, arch, vault" (12c.), from Latin arcus "a bow, arch," from PIE root *arku- "bowed, curved" (cognates: Gothic arhvazna "arrow," Old English earh, Old Norse ör; also, via notion of "supple, flexible," Greek arkeuthos, Latvian ercis "juniper," Russian rakita, Czech rokyta, Serbo-Croatian rakita "brittle willow"). Electrical sense is from 1821.
