Key split with club that's washed up (9)
I believe the answer is:
driftwood
'that's washed up' is the definition.
I can't judge whether this definition defines the answer.
'key split with club' is the wordplay.
'key split with' becomes 'drift' (I can't explain this - if you can you should believe this answer much more).
'club' becomes 'wood' (wood is a kind of club).
'drift'+'wood'='DRIFTWOOD'
Can you help me to learn more?
(Other definitions for driftwood that I've seen before include "found washed up on a beach?" , "items washed up?" , "What beachcomber found" , "box, perhaps left by water" , "Flotsam" .)