I found this website.
Your Rights and Responsibilities as a Minor Page 5
You can click on home or enter a search but I think the page answers your question.
Since your son is 18 and no longer considered a minor, by law you do not have to feed and shelter him if you so choose. I am assuming that he does not pay you any rent to live there. If he does, then you would have to evict him as per whatever the state dictates to evict a tenant. You can do a search on that by entering Tennessee Eviction Laws on "Google" or whatever search engine you use, and see what pops up.
If your son does not pay rent, I do have a suggestion if you really are serious about this.
Give him an ultimatum and put a specified time frame on it.
For example, tell him you and your wife are unwilling to support him for the rest of his life if he continues to live the way he has. Let him know that under the law, since he has turned 18 you are under no obligation. Then tell him that you
are willing to support him if he chooses to go to college and maintain at least a ___ (2.5,? Up to you to choose) grade point average. If his grade point average does not meet the outlined expectations, he is to understand that he must leave your home. If he chooses to get a job, give him ___ days (30, 60, 90,. - whatever you feel is realistic and fair), to get one. Once he gets a job, he is to pay $___ ($250?? Again up to you to choose) per month for rent and food. He is responsible to do his own laundry and clean up after himself as if he were a paying tenant in your home.
If he does not stick to the agreed time frame, he is to understand that he must leave your home.
He needs to understand that life is made up of options and choices and, he is the one responsible for making those choices for himself, not you.
Write a contract between yourselves and your son, including your expectations and deadlines. Make him sign it. He needs to see that you are serious and that you will not put up with his lounging around, doing drugs, staying out all night with friends,. In other words, playtime is over.
I would buy a wall calendar and place it in a prominent place in your home with the date circled in bold black marker and the expectation for that date that you have listed in your contract.
This will make everything you are saying an absolute reality to him and you need to make it clear that the ultimate decision based upon the options that you give him, is his, and his alone to make. Keep pointing out the calendar as the hard evidence that you are not playing around and the clock is ticking.
If this doesn't light a fire under his butt, then you have to decide if you want to follow through on your threat.
Please remember, this is only a suggestion. It is what I would probably do if I was in your situation. Speak to some of your friends. Maybe they have other options, suggestions, or add ons.
Good Luck!