Crossword Genius

Ash found on the beach? (9)

Ross

I believe the answer is:

driftwood

I'm a little stuck... Click here to teach me more about this clue!

'ash' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Maybe they are linked in a way I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for driftwood that I've seen before include "box, perhaps left by water" , "Washed up pieces of tree" , "What beachcomber found" , "items washed up?" , "Timber, etc, on the sea" .)

I've seen this clue in The Guardian.
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