A yacht going astray in China (6)
I believe the answer is:
cathay
'china' is the definition.
(historical name for China)
'a yacht going astray in' is the wordplay.
'going astray' indicates an anagram.
'in' is an insertion indicator.
'yacht' with letters rearranged gives 'cathy'.
'a' placed into 'cathy' is 'CATHAY'.
(Other definitions for cathay that I've seen before include "China - antique" , "Name for China in medieval times" , "Old name for China with a feline to start" , "China long ago" , "Ancient China" .)