The most common and most likely answer to this crossword clue is the 5 letter word MODEL
I've seen this crossword clue in Financial Times
M
O
D
E
L
More clues leading to the result MODEL
- Perfect lines to fill little volume
- Way left to produce scaled-down version
- Catwalk artist is large on style
- Way short line is shown in pattern
- One demonstrating fashion line?
- Sitter partially fumbled, ominously knocked the wrong way
- Dummy and potty seldom deprived of son
- Dome’s shambolic, ludicrous opening, a perfect example
- Way line is displayed by mannequin?
- Fashion line for example
Buddy explains!

The straight part
We know that "Sitter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sitter = model.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 MODEL mean?
MODEL noun- A person who serves as a subject for artwork or fashion, usually in the medium of photography but also for painting or drawing.
- A person, usually an attractive female, hired to show items or goods to the public, such as items given away as prizes on a TV game show.
- A representation of a physical object, usually in miniature.
- A simplified representation used to explain the workings of a real world system or event.
- A style, type, or design.
- The structural design of a complex system.
- A successful example to be copied, with or without modifications.
- An interpretation function which assigns a truth value to each atomic proposition.
- An interpretation which makes a set of sentences true, in which case that interpretation is called a model of that set.
- An animal that is used to study a human disease or pathology.
- Any copy, or resemblance, more or less exact.
- In software applications using the model-view-controller design pattern, the part or parts of the application that manage the data.
- To display for others to see, especially in regard to wearing clothing while performing the role of a fashion model
- To use as an object in the creation of a forecast or model
- To make a miniature model of
- To create from a substance such as clay
- To make a model or models
- To be a model of any kind
- Worthy of being a model; exemplary.