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

• 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

As in Williams’ case, attorneys argued that a sweep had violated the plaintiffs’ Fourth Amendment rights protecting them from unreasonable search and seizure, as well as their 14th Amendment right to due process. —Ariane Lange, Sacbee.com, 24 Mar. 2026

That is ultimately what The Secret Garden is about—the stubborn, almost unreasonable insistence of living things to grow toward the light. —Literary Hub, 23 Mar. 2026

The Constitution’s Fourth Amendment protects against unreasonable searches and seizures, meaning that prolonged detention or invasive questioning typically requires reasonable suspicion or probable cause. —Hannah Hudnall, USA Today, 23 Mar. 2026

These are not unreasonable requests. —Ted G Callam, San Diego Union-Tribune, 23 Mar. 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