harmless, ineffective pill used in drug tests, which is given to a number of participants in the test instead of the real drug in order to provide a clinical contrast to the effects of the drug
In many clinical trials, antidepressant medications have been found to be less effective than a placebo.
placere (to please) (Latin)
split it like this PLACE-it takes the place of the actual substance. and BOgus. it doesn't do what the actual pill does. Thus PLACEBO is a bogus harmless pill which takes the place of the original.