- something that is believed to be true or probably true but that is not known to be true
- I made the assumption that he was coming, so I was surprised when he didn't show up.
- He will come home tomorrow. At least, that's my assumption.
- Many scientific assumptions about Mars were wrong.
- We are operating on/under/with the assumption that the loan will be approved. [=we are assuming that the loan will be approved; we are behaving as though we know that the loan will be approved]
- I'm telling you our arrival time on the assumption that you will check to see whether or not our flight is on time before you come to the airport.
- Her plan is based on the underlying assumption that the economy will improve in the near future.
- her assumption of the presidency
- the act of taking or beginning to have power, control, etc., in a job or situation
- the assumption of control/authority
- the buyer's assumption of debt