/ pləˈsiːbəʊ; NAmE -boʊ/ noun
( pl. -os ) a substance that has no physical effects, given to patients who do not need medicine but think that they do, or used when testing new drugs :
the placebo effect (= the effect of taking a placebo and feeling better)
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WORD ORIGIN
late 18th cent.: from Latin , literally I shall be acceptable or pleasing , from placere to please.