The most common and most likely answer to this crossword clue is the 6 letter word SULFUR
I've seen this crossword clue in The Guardian
S
U
L
F
U
R
Buddy explains!

The straight part
We know that "S" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case s = sulfur.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 SULFUR mean?
SULFUR noun- A chemical element (symbol S) with an atomic number of 16.
- A yellowish green colour, like that of sulfur.
- To treat with sulfur, or a sulfur compound, especially to preserve or to counter agricultural pests.
- Of a yellowish green colour, like that of sulfur.