a word that imitates or suggests the source of the sound that it describes, first used in around 1577 AD
A double-blind test, where some patients receive the treatment being examined, and others get a placebo. Neither the patients or the administrators of the treatment know who is in which group. In order for the treatment to be proved useful, it must produce results that are better than the placebo at a statistically significant level. It also involves making sure the beliefs or subconscious mind of the tester or evaluator cannot UN-intentionally affect the results as in "BIAS"(maintain an objective neutral point of view ). Actually, for healing modalities, you’d want at least 3 groups. Group1 does the healing modality, Group2 goes through the motions of the healing modality and Group3 receives conventional treatment or placebo.
"Quack" derives from the 17th century word "quacksalver", in turn from the Dutch word kwakzalver (hawker of salve). Both "quack" and "kwak" originate from the Middle Dutch quacken (to brag or boast). Quacksalvers would appear in town market's offering cure-alls (Snake Oil salesman) in bottles to anyone gullible to part with their money.
 One falsely claiming to possess medical or other skills, especially one who dispenses potions, ointments, etc. supposedly having curative powers.
The day after I read this I noticed Negative ION Bracelets at the mall.