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

The standard is very low, and that is 'more probable than not' that this child may have been put in an unreasonable risk of harm. — Erin Moriarty, CBS News, 9 Aug. 2026

In such an environment, Fundstrat’s Tom Lee has argued that the S & P 500 can climb to 8,000 over the next few weeks, a level that is not too unreasonable given that the broader index was last trading around 7,750 — only 3% away. — Sarah Min, CNBC, 7 Aug. 2026

Hundreds of thousands of property and business owners saw their assessed values raised by more than 15% either in 2023 or 2025, leading to inflated property tax bills that many have called unreasonable or unfair. — Ilana Arougheti, Kansas City Star, 5 Aug. 2026

Which is not entirely unreasonable given this very specific set of circumstances. — Brian Grubb, Vulture, 3 Aug. 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