Merciless one (4)
I believe the answer is:
ming
'merciless one' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ming that I've seen before include "Chinese dynasty noted for porcelain" , "An imperial Chinese dynasty" , "Mediaeval Chinese dynasty, ware" , "Porcelain associated with Chinese dynasty" , "Famous porcelain from China 14th-17th centuries" .)