The most common and most likely answer to this crossword clue is the 6 letter word SVELTE
I've seen this crossword clue in The Guardian
S
V
E
L
T
E
More clues leading to the result SVELTE
- Slender girl’s bottom pinched by horse doctor in the middle of Ossett
- Trim so veil extends lower than eyes to start with
- Large Steve could be slim
- Slinky five in sleet, dancing!
- Graceful and selective when mixed with crushed ice
- Slim elves play around a square
- Elegantly slender forms loveliest after massage with oil
- Restyle Elvis occasionally, coming back lithe …
- Tighten your belt and behind — adults are going to be slender
- Slim Scandinavian, typically, almost reaching officer grade at last
Buddy explains!

The straight part
We know that "Slim" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case slim = svelte.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 SVELTE mean?
SVELTE adjective- Attractively thin; gracefully slender.
- Refined, delicate.