Castaway's spot (4)
I believe the answer is:
isle
'castaway's spot' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for isle that I've seen before include "It lies badly in water" , "Small area of land in water" , "-- of Dogs, area of London" , "Sea-girt area" , "Wight, Man or Skye" .)