The origin of a term is often vague or obscure. Many of them come into the American English language from rural England or primitive, back-country America where words reflect what one sees or hears. Such may be the case with the term clean as a whistle. The matter is debated (not with much fury I suspect) and we are left to our own choice to determine the origin which fits our needs.
It’s clear that this term was around in the 18th century literary hey-day of England when writers like Robert (Bobby) Burns used it in one of his poems. But even before that, there is some speculation that it refers to the sound a sharp sword makes as it falls upon the soon-to-be-beheaded criminal. In 2015 that is too cruel a recent memory for me to want to claim it, although there may be some truth to it as an origin. Burns’ poem “Earnest Cry” uses the term “as toon’s a whistle“…the term toon being a Middle English word for clear or clean.
Others say that it has to do with the fact that when a whistle is carved from a branch of a tree or bush it must have clear, clean “inners” in order to produce a clear, clean sound. If there is any debris left in the routed chamber of the whistle, the sound will be impure.
All of these explanations, or none of them, may be the actual origin. But the point becomes obvious as the term is used to indicate (in this day and age) that something is pure, clean, and unadulterated…like when someone or something whistles. There is nothing sharper or more piercing that a well-executed whistle of the sort that calls dogs from the fields or children from their play.
We know that in a sporting event the crowd may have any number of sounds, including that irritating vuvuzela horn that emerged in the World Cup games in Africa several years ago. Sometimes the sounds of the horns, bells, buzzers, drums, and other instruments, including the voice, drown out the sounds on the playing field. Therefore, officials of such a game have the privilege and right to the use of a common whistle, whose sharp, clear sound will cut through the other noises of the stadium. It is a bright, upper-range sound unlike any other except the human replica which is banned from fan seating. When the whistle blows, play stops, despite the other ambient sounds.
It is basically the same thing for the whistle of a police officer. It cuts through sounds of traffic, screaming, and other urban noise to signify that there is something amiss and help is needed. For that reason, young women on campuses have been taught to carry a metal whistle which can be used if attacked. It is far more effective than the human voice in calling for help.
So, to be clear as a whistle means to be easily detected and unable to be ignored. Therefore, the term moves away from a physical device, such as a police whistle, and becomes metaphorical in literature to mean that a subject is so obvious that it is clear as a whistle. There is no way to ignore it. And one can’t plead that it is unable to be understood.
Image Credit: A child’s dream