unreasonable

adjective

un·​rea·​son·​able

ˌən-ˈrēz-nə-bəl, 

-ˈrē-zᵊn-ə-bəl 

1

a

: not governed by or acting according to reason

unreasonable people

b

: not conformable to reason : absurd

unreasonable beliefs

2

a

: exceeding the bounds of reason, appropriateness, or moderation

working under unreasonable pressure

an unreasonable restraint of trade

b

: lacking justification

an unreasonable inference

unreasonableness

ˌən-ˈrēz-nə-bəl-nəs, 

-ˈrē-zᵊn-ə-bəl- 

noun

unreasonably

ˌən-ˈrēz-nə-blē, 

-ˈrē-zᵊn-ə-blē 

adverb

Synonyms of unreasonable

• unwarranted
• irrational
• unfounded
• baseless
• unsupported
• groundless
• invalid
• unsubstantiated
• unnecessary
• unreasoned
• absurd
• false
• illogical

Examples of unreasonable in a Sentence

I told him that I wouldn't pay unless he sent me a replacement. Am I being unreasonable?

You are entitled to compensation for unreasonable delays.

Recent Examples on the Web

But several individually reasonable events, viewed together and over time, can tell an unreasonable story. — Shahen Minasyan, Forbes.com, 24 Sep. 2026

At the outset of the Biden administration in January 2021, NASA was still targeting a 2024 lunar landing, even though this was widely seen as unreasonable. — Eric Berger, ArsTechnica, 23 Sep. 2026

But Universal Ostrich Farms, a beak-to-tail-feathers operation that has sold everything from the animals’ meat to salves rendered from their fat, chose to challenge the order as unfair and unreasonable. — J. B. MacKinnon, Harpers Magazine, 22 Sep. 2026

Vagmaxxing seems the logical offshoot of a trend that prizes unreasonable, unrealistic body modification to the point of impossible AI perfection and transhumanism—scary enough! — Valerie Monroe, Allure, 21 Sep. 2026

Word History

First Known Use

14th century, in the meaning defined at sense 1a

Legal Definition

unreasonable

adjective

un·​rea·​son·​able

: not reasonable : beyond what can be accepted: as

a

: clearly inappropriate, excessive, or harmful in degree or kind

an unreasonable delay

an unreasonable restraint of trade

b

: lacking justification in fact or circumstance

an unreasonable inference

especially : irrational sense b

the agency decision was unreasonable

c

: not supported by a warrant or by a valid exception to a warrant requirement (as when there is reasonable suspicion) and therefore unconstitutional

the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated

—U.S. Constitution amend. IV

see also search, seizure

unreasonableness noun

unreasonably adverb