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

: exceeding the bounds of reason or moderation

working under unreasonable pressure

unreasonableness

ˌən-ˈrēz-nə-bəl-nəs

-ˈrē-zᵊn-ə-bəl- 

noun

unreasonably

ˌən-ˈrēz-nə-blē

-ˈrē-zᵊn-ə-blē 

adverb

Synonyms

• irrational
• unwarranted
• unfounded
• baseless
• unsupported
• invalid
• unnecessary
• groundless
• unsubstantiated
• 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

Russia is trying to paint Ukraine as the unreasonable party in negotiations, Ferris said. —Lauren Kent, CNN Money, 12 Sep. 2025

We're protected from unreasonable searches and seizures. —Adeola Adeosun, MSNBC Newsweek, 9 Sep. 2025

Darryl Morin, national president of Forward Latino, a Latino advocacy group based in Franklin, Wisconsin, said the decision erodes Fourth Amendment protections against unreasonable search and seizure. —Francesca Pica, jsonline.com, 9 Sep. 2025

This is a crude and unreasonable attempt to make the discussion into an all-or-nothing affair. —Lance Eliot, Forbes.com, 7 Sep. 2025

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