Latin for 'I shall please' — originally the opening word of a psalm in the Catholic Office of the Dead. By Chaucer's time, 'singing placebo' meant flattery. Medicine adopted it in 1785 for treatments given to please rather than cure, sharing a root with 'please', 'placid', and 'placate'.
A substance with no therapeutic effect, used as a control in testing new drugs; more broadly, a treatment given to satisfy a patient's expectation of being treated.
From Latin 'placēbō', the first person singular future indicative of 'placēre' (to please): 'I shall please'. The word entered English through the Catholic Office of the Dead, where the antiphon for Vespers began with 'Placebo Domino in regione vivorum' ('I shall please the Lord in the land of the living', Psalm 116:9 in the Vulgate). By the 14th century, 'to sing placebo' meant to flatter or say what someone wanted to hear. The medical sense