“Willy-nilly” has two meanings. The first is “whether it is with or against your will,” and the second, which we tend to use today, is “in an unplanned, haphazard fashion.”
One of the first citations for “willy-nilly” in the Oxford English Dictionary is from 1608. The Barnhart Concise Dictionary of Etymology says it’s a contraction of “will I, nill I” or “will he, nill he” or “will ye, nill ye.” But the phrase dates back at least a thousand years, with the earliest known version being the Old English text, Aelfric’s Lives of Saints, circa 1000 CE.
Shakespeare used it in The Taming of the Shrew, in 1596. Petruchio says to Katharina:
“Thus in plain terms: your father hath consented
That you shall be my wife; your dowry ‘greed on;
And, Will you, nill you, I will marry you.”
Later, the expression also appears as “nilly willy” or “willing, nilling,” or even, in a perhaps pompous version, “william nilliam.” The early meaning of the word “nill” is key. In early English, “nill” was the opposite of “will,” a contraction of “ne will.” In other words, “will” meant you wanted to do something, and “nill” meant you wanted to avoid it. Thus, combining the willing and unwilling expressions into “willy-nilly” expressed the idea that it didn’t matter one way or the other.
The second meaning, “in an undecided, haphazard manner,” derives from the first. The “this way, then that way” imagery of willy-nilly behavior fits with the current meaning of “haphazard.”
The “undecided” meaning of the expression seems to have given birth to the later “shilly-shally.” The Oxford English Dictionary cites Sir Walter Besant’s novel The Orange Girl, 1898: “Let us have no more shilly shally, willy nilly talk.”
There are literally thousands of 18th and 19th century pre-datings of the phrase, in various newspapers and works of literature; for example, The Adventures of Dick Hazard, 1755:
“Where I quartered, a good buxom Widow kept the house; and I had her before I was ten days in town —D— me. She knew things better than to stand Shilly Shally.“
But there is a third meaning for “will-nilly.” Several years ago, the Washington Post asked readers to take any word from the dictionary, alter it by adding, subtracting, or changing one letter and supply a new definition. For example: “Intaxication,” meaning euphoria at getting a tax refund, which lasts until you realize it was your money to start with.
Here’s my favorite: Willy-nilly: impotent.