/pleuh see"boh/ for 1; /plah chay"boh/ for 2 , n. , pl. placebos, placeboes .
1. Med. , Pharm.
a. a substance having no pharmacological effect but given merely to satisfy a patient who supposes it to be a medicine.
b. a substance having no pharmacological effect but administered as a control in testing experimentally or clinically the efficacy of a biologically active preparation.
2. Rom. Cath. Ch. the vespers of the office for the dead: so called from the initial word of the first antiphon, taken from Psalm 114:9 of the Vulgate.
[ 1175-1225 for def. 2; 1775-85 for def. 1; ME placebo I shall be pleasing, acceptable ]