He wrote about a castaway's half-dead enemy (5)
I believe the answer is:
defoe
'he wrote' is the definition.
(I've seen this before)
'half-dead enemy' is the wordplay.
'half' indicates taking half.
'enemy' becomes 'foe' (I've seen this before).
'dead' cut in half is 'de'.
'de'+'foe'='DEFOE'
'about a castaway's' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for defoe that I've seen before include "Daniel -, Moll Flanders author" , "Daniel, author of Robinson Crusoe" , "pamphleteer and novelist" , "Gulliver author" , "18th-century author" .)