sup·po·si·tion 
/ˌsʌpəˈzɪʃən/ noun
plural sup·po·si·tions /ˌsʌpəˈzɪʃən/ noun : an idea or theory that you believe is true even though you do not have proof [count] ▪ an idle supposition [=assumption] ▪ a supposition that proved correct ▪ Her decision was made on the supposition that we would all agree. [=when she made her decision she supposed/assumed that we would all agree] [noncount] ▪ This is just idle supposition.
