Witches' pot (8)
I believe the answer is:
cauldron
'witches' pot' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for cauldron that I've seen before include "Witches' vessel" , "Witch's brewing pot" , "Large kettle" , "Very large metal pot for boiling" , "Witches' pot" .)