Resentment (also called ranklement or bitterness) is a complex, multilayered emotion that has been described as a mixture of disappointment, disgust and anger. Other psychologists consider it a mood or as a secondary emotion (including cognitive elements) that can be elicited in the face of insult and/or injury.
Inherent in resentment is a perception of unfairness (i.e. from trivial to very serious), and a generalized defense against unfair situations (e.g. relationships or unfavourable circumstances).
The word originates from French "ressentir", re-, intensive prefix, and sentir "to feel"; from the Latin "sentire". The English word has become synonymous with anger, spite, and holding a grudge.