1. （用于测试新药效力的）无效对照剂；（用以安慰想象自己得病的人的）安慰剂
A placebo is a substance with no effects that a doctor gives to a patient instead of a drug. Placebos are used when testing new drugs or sometimes when a patient has imagined their illness.

1. (Roman Catholic Church) vespers of the office for the dead

2. an innocuous or inert medication
given as a pacifier or to the control group in experiments on the efficacy of a drug