Definition · Plain-language
Idiom
An idiom is a fixed phrase whose overall meaning cannot be deduced from the literal meaning of its individual words, such as "kick the bucket".
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Meaning beyond the literal words
An idiom is a phrase that the speakers of a language understand by convention rather than by adding up its parts. If you took "raining cats and dogs", "spill the beans" or "let the cat out of the bag" word by word, you would reach the wrong meaning entirely; each is understood as a whole to mean, respectively, raining heavily, revealing a secret, and disclosing something hidden. This non-literal, non-compositional quality is the defining feature of an idiom. Because their meaning is agreed rather than deducible, idioms are a notorious difficulty for language learners and for machine translation, which often renders them literally and nonsensically.
Idioms are fixed expressions
Most idioms are frozen in form: you cannot usually substitute a synonym or change the grammar without breaking them. "Kick the bucket" cannot become "kick the pail", and "spill the beans" cannot become "spill the peas", even though the substitutes mean the same literally. This fixedness distinguishes idioms from ordinary figurative language, which a speaker invents freely. Some idioms do allow limited variation, and many can be inflected for tense ("she spilled the beans"), but the core words stay put. The phrase functions almost as a single long word with one agreed meaning.
Idioms and figurative language
Idioms are part of the broader category of figurative language — language that means something other than its literal sense — alongside metaphor, simile and hyperbole. Many idioms began as vivid metaphors that hardened into set phrases over time, so their original image is often forgotten: few people picturing "the bucket" know the phrase’s disputed origins. Every language has its own stock of idioms tied to its culture and history, which is why idioms rarely translate directly. For deeper coverage of metaphor, simile and related devices, see the literary-devices treatment of figurative language.
Key facts
At a glance
- Definition: a phrase whose meaning is not deducible from its words
- Key feature: figurative and non-compositional meaning
- Form: usually fixed — words cannot be freely swapped
- Example: "kick the bucket" means to die
- Relation: a type of figurative language
- Note: idioms are culture-specific and resist literal translation
Common misconceptions
What people often get wrong
Often heard: You can work out an idiom’s meaning from its individual words.
Actually: By definition you cannot. The meaning of an idiom is figurative and agreed by convention — "kick the bucket" means to die and has nothing to do with a literal bucket. This non-literal meaning is what makes it an idiom.
Often heard: You can swap words in an idiom for synonyms.
Actually: Idioms are usually fixed expressions. "Spill the beans" cannot become "spill the peas" without losing the idiomatic meaning, even though the words mean the same literally.
Often heard: An idiom is the same as a metaphor.
Actually: An idiom is a fixed, conventional phrase; a metaphor is a freely created comparison. Idioms are one part of the wider family of figurative language, which also includes metaphor and simile.
Going deeper
