Macbeth's old hag endlessly goes around this (8)
I believe the answer is:
cauldron
'this' is the definition.
The definition suggests a singular noun which matches the answer.
'macbeth's old hag endlessly goes around' is the wordplay.
'macbeth' becomes 'auld' (I am not sure about this - if you are sure you should believe this answer much more).
'old hag' becomes 'crone' (I've seen this in another clue).
'endlessly' means to remove the last letter.
'goes around' means one lot of letters goes inside another.
'crone' with its final letter taken away is 'cron'.
'auld' going inside 'cron' is 'CAULDRON'.
Can you help me to learn more?
(Other definitions for cauldron that I've seen before include "Witches' pot" , "Very large metal pot for boiling" , "Witches' vessel" , "Large kettle" , "Witch's brewing pot" .)