Confine boiler (6)
I believe the answer is:
kettle
'boiler' is the definition.
(I know that boiler can be written as kettle)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for kettle that I've seen before include "Vessel for boiling liquids" , "Kitchen container and type of drum" , "One boiled" , "Spouted vessel" , "Water boiler" .)