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

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

5

: the taking over of another's debts

6

: arrogance, pretension

Synonyms

• 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

Around the league, there was an assumption that the move was temporary and that he would soon be cut loose to join a playoff-caliber roster. —Grant Afseth, MSNBC Newsweek, 24 Sep. 2025

When young workers are screened out by ageist assumptions, firms buy more labor on the open market at premium prices, turnover rises, tacit knowledge leaks, and innovation slows. —Jennifer Moss, Fortune, 24 Sep. 2025

But those who have lived with this disease know that assumption is misleading. —Lauryn Higgins, Flow Space, 24 Sep. 2025

These findings highlight a more significant aspect of how AI systems encode and perpetuate cultural assumptions, as well as where decoding errors might occur in the human reader's mind. —ArsTechnica, 23 Sep. 2025

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