Is this a Discrimination or Defamation case?

Another employee and I was up for a promotion and only one of us could get it. I fell sick and was out for a week and a half. When I came back to work I was approached by my Boss and she told me that she wanted to terminate me for using the "F" word against employees and customers. I told her that is not in my daily vocabulary and she told me she had witnesses and customer complaints. She also told me that no-one liked working with me either. Then she preceded to tell me that she was not going to fire me because she had no-one else to work and needed me. She also told me if I tell anyone I will be automatically fired! I am torn up about this and this cost me my promotion. I am a GOD fearing woman and a hard worker. I did secretly talk to some employees and they told me they would be a witness that I do not use that language. The other woman got the promotion and I am on the firing line and now constantly watched. I hurt inside everyday I go to work. I did like my job until this co-worker lied about me and I do not know what the Boss has on me. I am a single granny raising a disabled child and need the income. So I do not have the option of quitting. I am looking for another job though just in case things go south.