Piece of furniture that's not finished first? Give over! (6)
I believe the answer is:
desist
'give over' is the definition.
(thesaurus)
'piece of furniture that's not finished first?' is the wordplay.
'piece of furniture' becomes 'desk' (desk is a kind of piece of furniture).
'that's not finished' means to remove the last letter.
'first?' becomes 'ist'.
'desk' with its last letter taken away is 'des'.
'des'+'ist'='DESIST'
(Other definitions for desist that I've seen before include "'Stop, give over (6)'" , "Stop, discontinue" , "Stop, don't continue" , "Stop (doing something)" , "Eject; annoyed" .)