placebo [L18th] In Latin placebo means ‘I shall be acceptable or pleasing’. Doctors have probably always prescribed some drugs just to keep a patient happy, and used the term placebo for these as far back as the late 18th century. Researchers testing new drugs give some participants substances with no therapeutic effect to compare their reactions to those who have genuinely been treated: such a substance is also a placebo. Results may be confused, though, by the placebo effect [E20th], in which the person’s belief in the treatment brings about beneficial effects that have nothing to do with the properties of the placebo they have taken. Placid [E17th] comes from the same Latin root, along with words under *please.