Cathy lost boat (5)
I believe the answer is:
yacht
'boat' is the definition.
(yachting is a kind of boating)
'cathy lost' is the wordplay.
'lost' indicates an anagram.
'cathy' is an anagram of 'YACHT'.
(Other definitions for yacht that I've seen before include "Kind of boat" , "Sailing craft" , "Sailing or motor vessel for cruising or racing" , "Light sailing vessel" , "Luxury purchase" .)