As clean as a whistle
This is another of those idioms that take the form of a simile. We use it to denote that something has been done completely, neatly, thoroughly or with great skill. If you were to be beheaded you would hope that the blade would remove your head as clean as a whistle. Alternatively, it describes something that is extremely clean.
But why a whistle and why clear?
As with many an etymological enquiry, there is no consensus and the best we can do is pick our way through the evidence. The earliest usage I can find in print appears in Joseph Reed’s The Register Office: A Farce of Two Acts, published in 1761. One of the characters, Gulwell, bemoans his financial disaster; “So Dick is unshipp’d and the Bond not worth a farthing! – I have lost the five hundred pounds as clean as a whistle.” There are two things to note; clearly Reed felt he could use the phrase without any gloss and that it means completely or entirely, perhaps with a hint of rapidity.
William Carr in his The Dialect of Craven, in the West Riding of the County of York, published in 1821, confirmed this usage when he defined our phrase as “a proverbial simile, signifying completely, entirely: as, “I’ve lost my knife as clean as a whistle.” Unhelpfully, though, he adds, “but I know not the propriety of the simile.”
But then we have to take into account a passage in Robert Burns’ poem The Author’s Earnest Cry and Prayer from 1786. There he writes “Her mutchkin stowp as toom’s a whissle.” Translated for delicate Sassenach ears, it means “Her pint bucket is as empty as a whistle” and has given rise to the supposition that in order to make a note, never mind a bright, clear sound, a whistle needs to be free of spittle. In other words, clean.
Another theory is that the phrase is intended to conjure up the whistling of a sword as it moves through the air. Swordsmen were encouraged to let their tutor hear their sword whistle. It was used to denote a clean cut in the 19th century, as it is today, as this quote from 1849 shows; “a first rate shot. [His] head taken off as clean as a whistle.” But more prosaically, Rick Wiebe in his Whittlin’ Whistles, published in 2012, describes how to make a slip-bark whistle, adding that clean as a whistle relates to the smooth cuts necessary to make one and without which the whistle would not work.
Beguiling as this theory might be, it doesn’t take account of the 18th century usage which was clearly intended to convey the sense of completeness. There was a variant around at the time, clear as a whistle, which replicating the distinct and recognisable sound of the everyday instrument meant unmistakable or unambiguous. It is not inconceivable to suppose that clear mutated to clean or that the whistle was used as a simile to reflect certainty or completeness. Even Robbie Burns’ use of a Scottish variant can be seen to fit this interpretation. The woman’s bucket was completely empty.
The usage of clean as a whistle to mean clean or pure is a later development, not the original sense.
This may all seem to you to be about as clear as mud but I think we are on the right track.