/əˈsjuːm/
[verb] To accept something as true without having proof of it, or to take on a responsibility, role, or position.
To 'assume' once meant to physically take something up into the sky — like the Virgin Mary being lifted into heaven.
The word 'assume' travels to us from the Latin verb 'assumere', which was built from two parts: the prefix 'ad-' (meaning 'to' or 'towards') joined to 'sumere' (meaning 'to take'). So the original Latin idea was simply 'to take to oneself' — a very physical, concrete action of picking something up or drawing it in. The root 'sumere' itself came from an even older combination: 'sub-' (under) and 'emere' (to take or buy), making 'assume' a word with layers of taking built right into its bones.
When Latin 'assumere' passed into Middle English during the 15th century, it arrived carrying a surprising first meaning. Its earliest use in English was theological — to describe the 'Assumption' of the Virgin Mary, her bodily ascent into heaven. To 'assume' was to be taken up, lifted into a higher place. You can still see this meaning alive in the word 'Assumption', the name of the Catholic feast day celebrated every August. The word had a kind of spiritual gravity before it became an everyday term.
From this celestial beginning, the word descended into more earthly territory. By the late 15th and early 16th centuries, English writers were using 'assume' to mean taking on a role, a quality, or a responsibility — putting something on like a garment. A king might 'assume the throne'; an actor might 'assume a disguise'. This sense of deliberately adopting something still sits at the heart of phrases like 'assume control' or 'assume a new identity', used comfortably in English today.
The meaning that most people think of first — to suppose something is true without checking — came slightly later, growing popular through the 17th and 18th centuries. This shift makes perfect sense when you think about it: if you 'take something to yourself', you are claiming it as yours, including an idea or a belief you haven't tested. To assume, in this sense, is to reach out and grab a conclusion before the evidence hands it to you. It is the intellectual equivalent of pocketing something that doesn't yet belong to you.
The Latin root 'sumere' also gave English several close relatives. Latin 'consumere' (to take completely) became the English 'consume'; Latin 'resumere' (to take again) travelled through Middle French as 'resumer' before becoming English 'resume'; and Latin 'praesumere' (to take beforehand) passed through Old French as 'presumer' into English 'presume'. All of these words carry that same ancient idea of taking — grabbing, claiming, or drawing something toward oneself — which shows just how deep and productive this little Latin root has been in shaping the English we speak today.