a substance given to someone who is told that it is a particular medicine, either to make that person feel as if they are getting better or to compare the effect of the particular medicine when given to others

She was only given a placebo, but she claimed she got better - that's the placebo effect. 只给她服用了安慰剂，但她说好一些了——这就是安慰剂的心理作用。

something that is given to try to satisfy a person who has not been given the thing they really want

These small concessions have been made as a placebo to stop the workers making further demands. 这些小让步就像安慰剂一样，可以避免工人们提出更多的要求。