irrational
ih-RASH-nuhl
Irrational (adj) means not based on logic or reason; unfounded or nonsensical. Example: “He had an irrational fear of elevators.”
adj
1
Not based on logic or reason; unfounded or nonsensical.
"He had an irrational fear of elevators."
"Her boss made an irrational decision that hurt the whole team."
"It is irrational to be afraid of a harmless spider on the wall."
2
In mathematics, describing a real number that cannot be written as a fraction of two whole numbers.
"Pi is a famous example of an irrational number."
"The square root of two is irrational, so its decimals never end or repeat."
"Our teacher asked us to prove that this particular number is irrational."
How to use irrational
Learner’s notesIn plain EnglishNot making logical sense — or, in math, a number that goes on forever without repeating and can't be written as a simple fraction.
Common pairings
irrational fear
irrational number
irrational behavior
Vocabulary Flow
Build your vocabulary from words like irrational.
Vocabulary Flow serves the next word, and the next — meaning, pronunciation and an example each time. Practice at your level, or learn English in your own language.
Start vocabulary practice
Word forms
- Plural
- irrationals
- Comparative
- more irrational
- Superlative
- most irrational
Fill the gap
Can you complete this real example?
He had an _____ fear of elevators.
Etymology
From Latin irratiōnālis, from ir- ("not") plus ratiōnālis ("rational").
Synonyms
View more →Antonyms
Related words
Rhymes for irrational
coronal
rational
diagonal
personal
seasonal
national
optional
regional
hormonal
hexagonal
fictional
emotional
See all rhymes for irrational →
Frequently asked questions
What does “irrational” mean?
The word “irrational” means not based on logic or reason; unfounded or nonsensical. In plain terms, not making logical sense — or, in math, a number that goes on forever without repeating and can't be written as a simple fraction.
How do you pronounce “irrational”?
“Irrational” is pronounced ih-RASH-nuhl (/ɪˈɹæʃ.(ə.)nəl/ in IPA).
How do you use “irrational” in a sentence?
Here is “irrational” used in a sentence: “He had an irrational fear of elevators.”
What part of speech is “irrational”?
“Irrational” is an adjective.
Where does the word “irrational” come from?
The word “irrational” comes from Latin. From Latin irratiōnālis, from ir- ("not") plus ratiōnālis ("rational").
Is “irrational” a common word?
“Irrational” is an uncommon word in modern English, usually learned at around the B2 level.
How many meanings does “irrational” have?
“Irrational” has 2 distinct senses listed in this dictionary. The most common is: not based on logic or reason; unfounded or nonsensical.
What is the difference between irrational and illogical?
Irrational describes something not based on logic or reason, often emphasizing emotion or fear over sense, such as an irrational fear. Illogical focuses more narrowly on a flaw in reasoning or argument structure, such as a conclusion that doesn't follow from its premises. Irrational is broader and often carries an emotional undertone that illogical lacks.
What is an irrational number in mathematics?
An irrational number is a real number that cannot be written as a fraction of two whole numbers, meaning its decimal representation never ends or repeats. Well-known examples include numbers like pi and the square root of two.
What is the difference between irrational and rational numbers?
Rational numbers can be expressed as a fraction of two whole numbers, such as 1/2 or 3, while irrational numbers cannot be written this way and have non-terminating, non-repeating decimal expansions. Every real number is either rational or irrational, but not both.
