1640s, first used in English by physician Sir Thomas Browne (1605-1682), apparently coined as Modern Latin electricus (literally "resembling amber") by English physicist William Gilbert (1540-1603) in treatise "De Magnete" (1600), from Latin electrum "amber," from Greek ēlektron "amber" (Homer, Hesiod, Herodotus), also "pale gold" (a compound of 1 part silver to 4 of gold); which is of unknown origin.
Vim illam electricam nobis placet appellare [Gilbert]
Originally the word described substances which, like amber, attract other substances when rubbed. Meaning "charged with electricity" is from 1670s; the physical force so called because it first was generated by rubbing amber. In many modern instances, the word is short for electrical. Figurative sense is attested by 1793. Electric light is from 1767. Electric toothbrush first recorded 1936; electric blanket in 1930. Electric typewriter is from 1958. Electric guitar is from 1938; electric organ coined as the name of a hypothetical future instrument in 1885.
1550s, "occurring or acting by turns, one after the other," present-participle adjective from alternate (v.). Electrical alternating current is recorded from 1839, an electrical current which flows alternately in opposite directions without interruption.