Vessel for boiling water (6)
I believe the answer is:
kettle
'vessel for boiling water' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for kettle that I've seen before include "Water boiler" , "Vessel for heating liquids" , "Check elements causing trouble in demonstration" , "Kitchen utensil and type of drum" , "Container for heating 10" .)