[ pluh-see-boh for 1; plah-chey-boh for 2 ]
/ pləˈsi boʊ for 1; plɑˈtʃeɪ boʊ for 2 /
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noun, plural pla·ce·bos, pla·ce·boes.
Medicine/Medical, Pharmacology.
  1. a substance having no pharmacological effect but given merely to satisfy a patient who supposes it to be a medicine.
  2. a substance having no pharmacological effect but administered as a control in testing experimentally or clinically the efficacy of a biologically active preparation.
Compare nocebo (def. 1).
Roman Catholic Church. the vespers of the office for the dead: so called from the initial word of the first antiphon, taken from Psalm 114:9 of the Vulgate.
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Origin of placebo

1175–1225 for def. 2; 1775–85 for def. 1; Middle English <Latin placēbō “I shall be pleasing, acceptable”
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use placebo in a sentence

British Dictionary definitions for placebo

/ (pləˈsiːbəʊ) /

noun plural -bos or -boes
med an inactive substance or other sham form of therapy administered to a patient usually to compare its effects with those of a real drug or treatment, but sometimes for the psychological benefit to the patient through his believing he is receiving treatmentSee also control group, placebo effect
something said or done to please or humour another
RC Church a traditional name for the vespers of the office for the dead

Word Origin for placebo

C13 (in the ecclesiastical sense): from Latin Placebo Domino I shall please the Lord (from the opening of the office for the dead); C19 (in the medical sense)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for placebo

[ plə-sēbō ]

A substance containing no medication and prescribed to reinforce a patient's expectation of getting well or used as a control in a clinical research trial to determine the effectiveness of a potential new drug.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for placebo

[ (pluh-see-boh) ]

A substance containing no active drug, administered to a patient participating in a medical experiment as a control.

notes for placebo

Those receiving a placebo often get better, a phenomenon known as the placebo effect.
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.