nounpl. no·ce·bos or no·ce·boes
A substance that causes undesirable side effects as a result of a patient's perception that it is harmful rather than as a result of a causative ingredient.
Origin of noceboLatin noc&emacron;b&omacron;, I will harm, first person sing. future tense of noc&emacron;re, to harm (on the model of placebo); see nek-1 in Indo-European roots.