[ plə'si:bəʊ ]
■ noun ( plural ~s )
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'.