The AMERICAN HERITAGE DICTIONARY defines placebo as:
A substance containing no medication administered for its psychological effect on a patient or an inactive substance used as a control in an experiment
The OXFORD DICTIONARY OF CURRENT ENGLISH defines it as:
Medicine with no physiological effect prescribed for psychological reason
or dummy pill used in a control trial.
I consider the latter more in keeping with what we consider in Homeopathy as placebo.
There will be others who may discuss this topic further.