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

Post-cyber asks whether our institutions, architectures and critical services can survive a world in which the assumptions beneath digital trust keep changing. — Peter Smulovics, Forbes.com, 12 Nov. 2026

With Mercury still retrograde in Scorpio, revisit the assumption underneath your original question. — Tarot.com, Chicago Tribune, 11 Nov. 2026

His analysis included direct medical expenses, public health spending and lost productivity, and examined how the estimates changed under different assumptions, including hospitalization rates. — Annika Kim Constantino, CNBC, 11 Nov. 2026

What Science Says About Blue-Eyed Horses and Blindness Scientific evidence challenges the broader assumption that blue-eyed horses are inherently more prone to vision problems. — MSNBC Newsweek, 10 Nov. 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