Not unfinished, ready to start and not (3)
I believe the answer is:
nor
'and not' is the definition.
(I've seen this before)
'not unfinished ready to start' is the wordplay.
'unfinished' means to remove the last letter.
'to start' suggests taking the first letters.
The initial letter of 'ready' is 'r'.
'not' with its final letter taken away is 'no'.
'no'+'r'='NOR'
(Other definitions for nor that I've seen before include "logic circuit" , "Negative conjunction" , "Common conjunction, goes with neither" , "In addition, not" , "And not; Norman (abbr.)" .)