placebo

Concise Oxford English Dictionary © 2008 Oxford University Press:
placebo /pləˈsiːbəʊ/

▶noun (pl. placebos)

• 1 a medicine or regime prescribed for the psychological benefit to the patient rather than for any physiological effect.

  ■ a substance that has no therapeutic effect, used as a control in testing new drugs.

• 2 a measure designed merely to calm or humour another.

– origin C18: from L., lit. ‘I shall be acceptable or pleasing’, from placere ‘to please’.