Cathy destroyed boat (5)
I believe the answer is:
yacht
'boat' is the definition.
(I know that yacht is a more specific form of the action boat)
'cathy destroyed' is the wordplay.
'destroyed' indicates an anagram.
'cathy' with letters rearranged gives 'YACHT'.
(Other definitions for yacht that I've seen before include "Light sailing vessel" , "Kind of boat" , "Luxury purchase" , "Cathy (anag.)" , "Pleasure-boat" .)