unreasonable

/ənˈrizɪnəbəl/

/ənˈrizənəbəl/

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."

Definitions of unreasonable

1. adjective

   beyond normal limits
   “unreasonable demands”

   synonyms: excessive, inordinate, undue

   immoderate

   beyond reasonable limits
2. adjective

   not reasonable; not showing good judgment
   synonyms:

   illogical, unlogical

   lacking in correct logical relation

   immoderate

   beyond reasonable limits

   irrational

   not consistent with or using reason

   counterintuitive

   contrary to what common sense would suggest

   indefensible, untenable

   (of theories, etc.) incapable of being defended or justified

   mindless, reasonless, senseless

   not marked by the use of reason

   undue, unjustified, unwarranted

   lacking justification or authorization

   antonyms:

   reasonable

   showing reason or sound judgment

   fair, just

   free from favoritism or self-interest or bias or deception; conforming with established standards or rules

   logical

   capable of or reflecting the capability for correct and valid reasoning

   rational

   consistent with or based on or using reason

   commonsense, commonsensible, commonsensical

   exhibiting native good judgment

   healthy, intelligent, level-headed, levelheaded, sound

   exercising or showing good judgment

   tenable, well-founded

   based on sound reasoning or evidence

   valid

   well grounded in logic or truth or having legal force