Castaway's shelter (3)
I believe the answer is:
hut
'castaway's shelter' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hut that I've seen before include "Small crude dwelling" , "Small shed for storing, say, garden tools" , "Small building or shelter" , "Small roughly-made house or shelter" , "Small house, shed" .)