I recently conducted an informal survey of a group of moderately intelligent college students and discovered, to my chagrin, that not one of them understood the full metaphorical import of the term weasel word. Several captured the connotation of the phrase: Weasels are sneaky; weasel words are used to avoid responsibility. But in view of the fact that weasel words have become a staple of contemporary political and commercial discourse, we should be clear on the meaning of this useful term.
The weasel, that least straightforward of beasts, will sneak into a bird's nest, bite a small hole in each egg, and suck out the contents, leaving the shell essentially intact. To a casual glance, the nest appears undamaged. But it is merely a facade; there is no substance behind the appearance. The eggs are merely empty shells.
Likewise, a single word or a brief phrase inserted into a meaningful sentence can suck all the meaning out while leaving the sentence superficially intact.
Response to a Speech
President Theodore Roosevelt's use of the term brought it to popular attention, though he did not coin it. We have this on the authority of William and Mary Morris in the "Morris Dictionary of Word and Phrase Origins." Roosevelt used the term in a speech in 1916. President Woodrow Wilson had proposed a system of "universal voluntary training." Roosevelt responded: "One of our defects as a nation has been the tendency to use what have been called weasel words. . . . If you use a weasel word after another there is nothing left of the other. Now you can have universal training or you can have voluntary training, but when you use voluntary to qualify universal, you are using a weasel word; it has sucked all the meaning out of universal. The two words flatly contradict each other."