Q: Can the words “colloquial” and “idiomatic” be used interchangeably? Is “idiomatic” somewhat more formal?
A: The terms “idiomatic” and “colloquial” widely overlap, but they aren’t identical. In general, a colloquialism is a spoken usage, but idioms can be found in speech as well as in writing, even in formal prose.
We wrote an extensive blog item last year about the term “idiomatic.” As we say in that posting, “Broadly speaking, an idiom is simply a peculiarity of language.”
An idiom might be an expression or grammatical construction that’s unusual in some way—peculiar to a language, a region, a dialect, a time period, or a group of people.
(For example, groups like doctors, mechanics, and teenagers all have their own vocabularies and expressions, which might be described as idiomatic.)
“Idiom” is a very broad term and can even refer to a distinctive literary expression. In our blog entry, for instance, we noted that in the 17th century John Donne called the biblical “amen” an idiom.
Some idioms aren’t easily translated, or can’t be taken literally. As the Oxford English Dictionary says, an idiom can be “a group of words established by usage as having a meaning not deducible from the meanings of the individual words.”
“Colloquial,” on the other hand, means characteristic of spoken language. So colloquialisms are more likely to be found in common speech than in formal written English.
The OED says the word “colloquial,” first used by Samuel Johnson in 1751, means “of or pertaining to colloquy; conversational.”
Both “colloquial” and “colloquy” (a conversation or dialogue) are derived from Latin, in which the prefix col- means together and the verb loqui means to speak
When “colloquial” is used in reference to words, phrases, and so on, the OED says, it means “belonging to common speech; characteristic of or proper to ordinary conversation, as distinguished from formal or elevated language. (The usual sense.)”
In summary, many colloquialisms can be described as idioms—like “I could care less,” which isn’t meant literally, or “that dress just isn’t you,” which wouldn’t make sense in another language.
But not all idioms are colloquial. Phrases like “weather permitting” or “on the other hand” are idioms commonly used in writing as well as speech.
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