IPA: /səˈpoʊzər/
KK: /səˈpoʊzər/
A person who makes an assumption or belief about something without having all the facts.
As a supposer, she often imagined different outcomes for the situation.
Supposer is formed from "sub-" (meaning under) and "ponere" (meaning to place). The word originally conveys the idea of placing something under consideration or assumption.
Think of placing an idea 'under' ('sub-') consideration — that's why 'supposer' means to assume or suppose something.