The first thing I would like for you to do is to look up the number for the nearest police or sheriff's office. Call them. Explain what is happening with your son and that you want to call them the next time he threatens you. Then pick a calm time when you and your son can talk, not fight. Explain to your son that you choose not to take his abuse any more; that you are willing to discuss issues but you will not be shouted at nor called names. Tell him firmly but calmly that if he chooses to call you names or shout at you that you will call the police. Then when he does (and he will to test you) call the police immediately.
You need support and some help in setting boundaries and consequences for your son. When you talk with the police, ask if there are any programs available for parents of out-of-control teens through the juvenile system. If not, you can call your local school or the state department of human services (child protection) to inquire about parenting classes. If you can, I might also suggest some family counseling even if you are the only family member who goes.
Please don't wait. You and your son need assistance as soon as possible.