also ikon, 1570s, "image, figure, picture," also "statue," from Late Latin icon, from Greek eikon "likeness, image, portrait; image in a mirror; a semblance, phantom image;" in philosophy, "an image in the mind," related to eikenai "be like, look like," which is of uncertain origin. The specific Eastern Church sense is attested from 1833 in English. Computing sense first recorded 1982.
Originally in reference to those in the Eastern Church in 8c. and 9c. whose mobs of followers destroyed icons and other religious objects on the grounds that they were idols. Applied to 16c.-17c. Protestants in Netherlands who vandalized former Catholic churches on similar grounds. Extended sense of "one who attacks orthodox beliefs or cherished institutions" is first attested 1842.