A part that is succeeding (6)
I believe the answer is:
sequel
'a part that is succeeding' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
This is all the clue.
Can you help me to learn more?
(Other definitions for sequel that I've seen before include "Consequence" , "Follow-up work" , "Something following a related event" , "Programme or work following on from another" , "Book following another" .)