How often do you hear an advert for a product say something like "This helps fight the symptoms of X" or this new drug "helps boost your immune system"? These adverts are using weasel words. They are very prevalent in alt-med where regulations and advertising rules stop them making explicit claims, so manufacturers and advertisers will use words that imply they work but don't actually state anything factually that can be counterclaimed. Words like 'help', 'assists', 'aids' and 'compliments', or phrases like 'works with' 'some people say', 'most people think', and 'researchers believe' don't actually tell you anything specific about what the product does and could apply to many things: 'most people think' chicken soup 'works with' your immune system and 'helps combat' a cold; which it does, simply by providing nutrients for your body - as does almost any food.
Other phrases such as 'up to' are weasley. Up to 20% off could mean 1% to 20% of the original price and something "lasting up to 20% longer" is hardly specific. Why use the word 'only' in advertising of not to mislead? What is the difference between something being £9.99, and ONLY £9.99? The latter implies that it is cheap but it doesn't actually state it. What does it mean when a package of nuts has the words '15% more' on it? 15% more than before? More than competitors?
Weasel words are used in place of specific testable claims in order to mislead through implication. Watch out too for: 'helped', 'may be', 'can be', 'tend to', 'we believe' and 'may promote / enhance / contribute to'. These are all good examples. You'll find them used by politicians, by advertisers and most egregiously by alt-med practitioners. A June 1900 issue of Century Magazine has been credited with the origin of the expression: “Weasel words are words that suck all of the life out of the words next to them just as a weasel sucks an egg and leaves the shell.”