assumption

noun

as·​sump·​tion ə-ˈsəm(p)-shən 

1

: a taking to or upon oneself

the assumption of a new position

2

: the act of laying claim to or taking possession of something

the assumption of power

3

a

: an assuming that something is true

a mistaken assumption

b

: a fact or statement (such as a proposition, axiom (see axiom sense 2), postulate, or notion) taken for granted

4

a

: the taking up of a person into heaven

b

Assumption : August 15 observed in commemoration of the Assumption of the Virgin Mary

5

: the taking over of another's debts

6

: arrogance, pretension

Synonyms of assumption

• theory
• premise
• hypothesis
• belief
• presumption
• presupposition
• hypothetical
• given
• postulate
• supposition

Examples of assumption in a Sentence

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.

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 buyer's assumption of debt

Recent Examples on the Web

Warren Buffett has long argued that the best boards are those where directors are willing to challenge assumptions rather than simply ratify them. —Jane Sadowsky, Fortune, 28 Mar. 2026

Seth Masket, a University of Denver political science professor, cautioned against making assumptions about the routes the candidates take to the ballot. —Nick Coltrain, Denver Post, 28 Mar. 2026

The senior Israeli security official who spoke anonymously with ABC News said Israel was working on the assumption that Iran had laid naval mines in the Strait of Hormuz. —Tom Soufi Burridge, ABC News, 27 Mar. 2026

There are so many women that are underestimated, so many women that present themselves in ways that people can find distracting or make assumptions about because of it. —Carly Thomas, HollywoodReporter, 27 Mar. 2026

Word History

Etymology

Middle English, from Late Latin assumption-, assumptio taking up, from Latin assumere — see assume

First Known Use

13th century, in the meaning defined at sense 4a

Phrases Containing assumption

• on/under/with the assumption
• self-assumption

Rhymes for assumption

• consumption
• presumption
• resumption
• subsumption
• gumption
• sumption

Kids Definition

assumption

noun

as·​sump·​tion ə-ˈsəm(p)-shən 

1

capitalized : August 15 observed as a church festival to mark the taking up of the Virgin Mary into heaven

2

a

: the act of taking upon oneself or taking possession of something

3

a

: the belief that something is true

b

: a fact or statement taken for granted