In the Wills and Trust arena, a "renunciation letter" typically is a letter signed by a person who is named in a Will or Trust to "give up" some claim to the estate of the person who has passed or from being the executor or executrix.In essence, a "renunciation letter" signed by a person is an agreement that the person signing the document is "giving up" some right that he or she may have. You have not specified what is being given up in your question with respect to your Wills and Trust question for me to be more specific in my answer.