suponer
/supoˈneɾ/ · A1 · verb
to suppose, to surmise, to assume, to guess, to imagine, to figure, to say, to take it
su + poner = sub + put: to put under, like English sup-pose
From Latin supponere, to place under. An assumption is an idea you put underneath your reasoning as its base. English suppose is the same word, so suponer = suppose. It conjugates like poner: supongo, supuse, supuesto.