The most common and most likely answer to this crossword clue is the 5 letter word IDIOM
I've seen this crossword clue in Financial Times
I
D
I
O
M
More clues leading to the result IDIOM
- Love encapsulated by one obscure turn of phrase
- Man following retired woman’s turn of phrase
- I'd recalled way of working one part of speech
- Turn of phrase in papers I'm carrying round
- One gets over wearing stupid expression
- Man absorbing woman’s artistic style
- I love to wear dumb expression
- I love wearing stupid expression
- Distinctive phrase fool finally changes
- Former dictator gets award for expression
Buddy explains!

The straight part
We know that "expression" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case expression = idiom.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does IDIOM mean?
IDIOM noun- A manner of speaking, a mode of expression peculiar to a language, person, or group of people.
- A language or language variety; specifically, a restricted dialect used in a given historical period, context etc.
- An established expression whose meaning is not deducible from the literal meanings of its component words, often peculiar to a given language.
- An artistic style (for example, in art, architecture, or music); an instance of such a style.
- A programming construct or phraseology that is characteristic of the language.