The origin of bangs (the word is occasionally found in the singular bang), referring to a fringe of hair falling over the forehead (especially if cut square), is uncertain. A common explanation, and the most likely one, is that bang(s) is short for bangtail. A bangtail is a horse's tail trimmed horizontally, so that the tail has a flat, even end, and hence a horse having such a tail. (By the early twentieth century, bangtail was used generically for 'a racehorse'.) This leaves the question of the origin of bangtail. The word bang 'to strike violently' or 'a sudden striking blow or sound' has an adverbial sense 'suddenly; abruptly; completely; directly', as in "he walked bang up to me," "a slam-bang effort," or, closer for our purposes, "to cut (something) bang off." Our bangs is probably from this adverbial use, one way or another: either it comes directly from this adverb, or bangtail itself is from this adverb and bang(s) is short for bangtail. The adverbial bang is recorded in the late eighteenth or early nineteenth century, depending on how you interpret the evidence. Bangtailed '(of a horse) having a bangtail' is found in the early 1860s, and bang 'fringe of hair' is first found in the late 1870s in America. http://www.randomhouse.com/wotd/index.pperl?date=19990112