I'm sorry this happened to you. It's absolutely intolerable.
Here's the course of action I would take:
1) Inform HR. They may ask you to file a formal complaint.
2) Inform your superior that you have already documented this with HR.
Your superior will probably ask you to sit through a mediation with the person who caused the offense. There, you'll be able to tell your boss that his use of the term is offensively and that it makes for a work environment that is negative. In this way, everything is documented with the department, with your boss and with HR. You get a way to confront your boss in a fair and safe manner, and the department cannot cover for him.
Good luck, and keep us updated!
Here's the course of action I would take:
1) Inform HR. They may ask you to file a formal complaint.
2) Inform your superior that you have already documented this with HR.
Your superior will probably ask you to sit through a mediation with the person who caused the offense. There, you'll be able to tell your boss that his use of the term is offensively and that it makes for a work environment that is negative. In this way, everything is documented with the department, with your boss and with HR. You get a way to confront your boss in a fair and safe manner, and the department cannot cover for him.
Good luck, and keep us updated!