From The Art and Popular Culture Encyclopedia
Resentment is an emotion of anger felt as a result of a real or imagined wrong done. Etymologically from "ressentir", French re-, intensive prefix, and sentir "to feel"; from the latin "sentire". The English word has become synonymous with anger and bitterness.
It can be an emotionally disturbing experience that is being felt again or relived in the mind. When the person feeling resentment is directing the emotion at himself it appears as remorse.