Disagreeable number just finished (3)
I believe the answer is:
not
'disagreeable number just finished' is the definition.
I can't judge whether this defines the answer.
'number just finished' is the wordplay.
'number' becomes 'no' (abbreviation for 'number').
'just finished' becomes 't' (I can't explain this - if you can you should give a lot more credence to this answer).
'no'+'t'='NOT'
Can you help me to learn more?
(Other definitions for not that I've seen before include "Having close-cut hair" , "Negatory word" , "In no way, never" , "Negation of what follows" , "Ton (anag.)" .)