The most common and most likely answer to this crossword clue is the 4 letter word MOSS
I've seen this crossword clue in The Guardian
M
O
S
S
More clues leading to the result MOSS
- Some blossoms on climbing plant
- Medical Officer’s son’s plant
- Clustering plant associated with Stirling, nominally
- None of this affects the Rolling Stones
- Racing driver appears in three seconds
- M&S clothing very large for fashion star
- ‘Plant‘ in security service denied promotion
- Racing driver once seen with model
- Fashion icon‘s very upset to wear two dress sizes
- Highland fog heads for mountains of southern Scotland
Buddy explains!

The straight part
We know that "fashion star" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fashion star = moss.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 MOSS mean?
MOSS noun- Any of various small, green, seedless plants growing on the ground or on the surfaces of trees, stones, etc.; now specifically, a plant of the phylum Bryophyta (formerly division Musci).
- A kind or species of such plants.
- Any alga, lichen, bryophyte, or other plant of seemingly simple structure.
- A bog; a fen.
- To become covered with moss.
- To cover (something) with moss.