placebo [plƏ séebō]

(plural pla-ce-bos or pla-ce-boes)

noun

1. prescription without physical effect: something prescribed for a patient that contains no medicine, but is given for the positive psychological effect it may have because the patient believes that he or she is receiving treatment

2. inactive substance: a preparation containing no active ingredients, given to a patient participating in a clinical trial in order to assess the performance of a new drug given to other patients in the trial

3. something done to placate somebody: something of no inherent benefit that is done or said simply to placate or reassure somebody

[13th century. >Latin, "I shall please"]

source: Encarta Dictionary