n. (pl. -os) 1 a a pill, medicine, etc. prescribed for psychological reasons but having no physiological effect. b a placebo used as a control in testing new drugs etc. c a blank sample in a test. 2 RC Ch. the opening antiphon of the vespers for the dead.
[ L, = I shall be acceptable or pleasing f. placere please, first word of Ps. 114:9 ]