Partly destroy a liner belonging to a monarch (5)
I believe the answer is:
royal
'to a monarch' is the definition.
(I've seen this before)
'partly destroy a liner belonging' is the wordplay.
'partly' indicates the answer is hidden within the clue (part of the clue is used).
'ROYAL' is hidden within 'destroy a liner belonging'.
(Other definitions for royal that I've seen before include "like The Grand Old Duke of York, perhaps" , "Relating to a monarch" , "Suitable for king or queen" , "Relating to kings/queens" , "Magnificent" .)