unreasonable
Americanadjective
-
not reasonable or rational; acting at variance with or contrary to reason; not guided by reason or sound judgment; irrational.
an unreasonable person.
-
not in accordance with practical realities, as attitude or behavior; inappropriate.
His Bohemianism was an unreasonable way of life for one so rich.
- Synonyms:
- nonsensical, stupid, absurd, preposterous, silly, foolish, senseless
-
excessive, immoderate, or exorbitant; unconscionable.
an unreasonable price; unreasonable demands.
- Synonyms:
- extravagant
-
not having the faculty of reason.
adjective
-
immoderate; excessive
unreasonable demands
-
refusing to listen to reason
-
lacking reason or judgment
Other Word Forms
- unreasonableness noun
- unreasonably adverb
Etymology
Origin of unreasonable
First recorded in 1300–50, unreasonable is from the Middle English word unresonabel. See un- 1, reasonable
Explanation
To be unreasonable means acting in an irrational way. Your expectation that your favorite team will win the Super Bowl every year is unreasonable. When someone's unreasonable, they're not using reason, or common sense, to make decisions or demands. Add the prefix un- to reasonable, "having sound judgment," and you get an adjective that's perfect for describing illogical behavior. It's often used for a certain kind of demanding stubbornness too: "It's completely unreasonable to make your server take your soup back five times to warm it up a little more."
Vocabulary lists containing unreasonable
"The Southpaw"
Looking to grow your vocabulary? Check out this interactive, curated word list from our team of English language specialists at Vocabulary.com – one of over 17,000 lists we've built to help learners worldwide!
Chronically Dolores
Interested in learning more words like this one? Our team at Vocabulary.com has got you covered! You can review flashcards, quiz yourself, practice spelling, and more – and it's all completely free to use!
Part 3 Vocabulary (Unit 2)
Want to remember this word for good? Start your learning journey today with our library of interactive, themed word lists built by the experts at Vocabulary.com – we'll help you make the most of your study time!
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
The country's parliament speaker Mohammad Bagher Ghalibaf posted on X that the "workable basis on which to negotiate" had already been violated, making further talks "unreasonable".
From Barron's • Apr. 9, 2026
That’s more than just innocence: A plaintiff must demonstrate that an arrest was inherently unreasonable and that police lacked even a reasonable suspicion of wrongdoing.
From Slate • Apr. 6, 2026
It’s not unreasonable for drivers to be upset about high fuel prices and for policymakers to want to tackle the issue.
From MarketWatch • Apr. 1, 2026
It’s where I watched Barack Obama get elected twice, the Lakers win back-to-back championships, and where I indulged in countless night caps and an unreasonable amount of all-you-can-eat split pea soup.
From Los Angeles Times • Mar. 26, 2026
“It’d be unreasonable for me to move to another chair,” Alex Van Ness pointed out.
From "Snow Falling on Cedars: A Novel" by David Guterson
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
