The most common and most likely answer to this crossword clue is the 8 letter word GRAPHITE
I've seen this crossword clue in The Sunday Telegraph
G
R
A
P
H
I
T
E
More clues leading to the result GRAPHITE
- Lead shot included in ammunition that scatters
- Jar containing letter that is covered in pencil
- Material for pencils Greek character put in jar
- Lead in pencil I gather erroneous — this the stuff?
- Writing hard stuff, Athenian letter put in jar
- Lead character in scrape
- Black lead letter in fireplace
- Grey substance Greek character found among the ashes?
- Lead Greek character drawn in by bars
- Success in Merlot, perhaps, offers lead for writer?
Buddy explains!
The straight part
We know that "Grey substance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case grey substance = graphite.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 GRAPHITE mean?
GRAPHITE noun- An allotrope of carbon, consisting of planes of carbon atoms arranged in hexagonal arrays with the planes stacked loosely, that is used as a dry lubricant and in "lead" pencils.
- Short for graphite-reinforced plastic, a composite plastic made with graphite fibers noted for light weight strength and stiffness.
- A grey colour.