Unclean. Impure, Same same. The Greek is akathartos which just means not ceremonial pure. The context is demons which are the fallen angels. Jesus called them impure spirits and depending upon which translation, were always evil spirits aka: demons. So yes, they are the same.
There are demons who never had a physical body of their own and there are impure spirits who had a physical body and went astray.
Often there are both in/around the same person. Believe what you want to believe, but if your loved one dies and their soul hangs around after they leave their physical body to help surviving children or family, their soul does not become a demon.
If we are in a physical body, we are sinners and impure. Spiritual growth and God’s Grace lifts us out of impurity.
Children are created pure, thus we must become like them to know God.
I have helped many, many souls of abortions cross over as they were hanging on to their mothers. They were pure but lost and needed guidance to go home. They were not demons just because they were spirits or souls without a physical body.