Show party promises to be endless (8)
I believe the answer is:
manifest
'show' is the definition.
(I know that manifest is a more specific form of the action show)
'party promises to be endless' is the wordplay.
I cannot really understand how this works, but
'party' could be 'fest' and 'fest' is present in the answer.
The remaining letters 'mani' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for manifest that I've seen before include "Express" , "Clear, obvious" , "Ship's document; plain" , "Obvious, like ship's cargo list" , "Become apparent" .)