Piece of wood is unacceptable for project (8)
I believe the answer is:
stickout
'piece of wood' is the definition.
The definition suggests a singular noun which matches the answer.
'unacceptable for project' is the wordplay.
'unacceptable' becomes 'out' (out can mean incorrect or inappropriate).
'for' means one lot of letters go next to another (I've seen this in other clues).
'project' becomes 'stick' (I can't explain this - if you can you should give a lot more credence to this answer).
'out' put after 'stick' is 'STICKOUT'.
'is' is the link.
Can you help me to learn more?
(Another definition for stickout that I've seen is " Don't give up - project".)