Quite done, at last... nothing is unfinished (6)
I believe the answer is:
enough
'quite' is the definition.
'last nothing is unfinished' is the wordplay.
'last' becomes 'e' (I've seen this in other clues).
'nothing' becomes 'nought' (synonyms).
'is unfinished' means to remove the last letter.
'nought' with its final letter taken away is 'nough'.
'e'+'nough'='ENOUGH'
'done at' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for enough that I've seen before include "Adequate amount to meet the purpose" , "Stop right now!" , "An adequate quantity" , "Not wanting" , "As much as necessary" .)