1. One who attacks and seeks to overthrow traditional or popular ideas or institutions.
2. One who destroys sacred religious images.

Word History: An iconoclast can be unpleasant company, but at least the modern iconoclast only attacks such things as ideas and institutions. The original iconoclasts destroyed countless works of art. Eikonoklastēs, the ancestor of our word, was first formed in Medieval Greek from the elements eikōn, "image, likeness," and -klastēs, "breaker," from klān, "to break." The images referred to by the word are religious images, which were the subject of controversy among Christians of the Byzantine Empire in the 8th and 9th centuries, when iconoclasm was at its height. In addition to destroying many sculptures and paintings, those opposed to images attempted to have them barred from display and veneration. During the Protestant Reformation images in churches were again felt to be idolatrous and were once more banned and destroyed. It is around this time that iconoclast, the descendant of the Greek word, is first recorded in English (1641), with reference to the Byzantine iconoclasts. In the 19th century iconoclast took on the secular sense that it has today, as in "Kant was the great iconoclast" (James Martineau).