(used in the passive) to expect or design; require or permit (followed by an infinitive verb): The machine is supposed to make noise. I'm not supposed to run fast.
Origin: 1275–1325; Middle English supposen < Old French supposer, equivalent to sup-sup- + poser to pose1; compare Medieval Latin suppōnere to suppose, Latin: to substitute, place below
early 14c., "to assume as the basis of argument," from O.Fr. supposer "to assume," probably a replacement of *suppondre (influenced by O.Fr. poser "put, place"), from L. supponere "put or place under," from sub "under" + ponere "put, place" (see position). Meaning "to admit