1
general::
1. Intended to; also, believed to, expected to. For example, This pill is supposed to relieve your pain, or You're supposed to be my partner. [Early 1300s.] 2. Required to, as in He is supposed to call home. [Mid-1800s] 3. not supposed to. Not permitted to, as in You're not supposed to smoke in here.
American Heritage Idioms
2
general::
Phrase(s): supposed to do something
expected or intended to do something; obliged or allowed to do something. • You’re supposed to say "excuse me" when you burp. • Mom says you’re supposed to come inside for dinner now., Phrase(s): Supposed to. [and] Someone or something is supposed to.
Someone or something is meant to do something. (Frequently, in speech, supposed is reduced to s’posed. The words someone or something can be replaced with nouns or pronouns, or used themselves.) • Mary: They didn’t deliver the flowers we ordered. Sue: Supposed to. Give them a call. • Sally: This screw doesn’t fit into hole number seven in the way the instructions say it should. Bill: It’s supposed to. Something’s wrong.
McGrawhill's American Idioms And Phrasal Verbs