Learner's definition of PRESUMPTION
1 [count] : a belief that something is true even though it has not been proved — often + that
The presumption is that the thief had a key to the store.
There was a widespread presumption that she would appoint him as her successor.
the presumption that all students learn in the same way
Thousands of people used this drug on the presumption that it was safe. [=they used it because they believed that it was safe]
2 law : an act of accepting that something is true until it is proved not true — often + of
3 [noncount], formal : willingness to do something without the right or permission to do it