clean as a whistle

Thoroughly or neatly done; also, pure, unsoiled. The early-nineteenth-century use of this term, which appears in William Carr’s The Dialect of Craven (1828) as a proverbial simile meaning “wholly” or “entirely,” was in such guise as “Head taken off as clean as a whistle” (W. S. Mayo, Kaloolah, 1849). Why this should be analogous to a whistle is not cer- tain. In the eighteenth century the simile was “clear as a whistle,” presumably referring to the pure sound produced by a whistle, relatively free of over- tones. From “clear” and “pure” to “clean” is not so very far. Another theory holds that “whistle” came from “whittle”—that is, clean as wood is after being whittled—but this analogy seems less likely.