When you postulate an idea or theory you suggest that it is true especially for the purposes of an argument or discussion. The word is mostly at home in formal and academic contexts, but don’t let that stop you from postulating, for example, that takeout for dinner makes sense given the cook’s delayed return home from work. The word postulate also functions as a noun referring to something that’s been postulated, as in “a theory based on disputed postulates.” Both verb and noun have their source in Latin postulare, meaning "to assume."