The word "indignant" comes from the Latin word "dignitatem," meaning "worth" or "dignity." The prefix "in-" in this case functions as a negative prefix, meaning "not." Therefore, "indignant" literally means "not worthy" or "not dignified."
It's important to note that the prefix "in-" can also be used to mean "into" or "on," but in the case of "indignant," it is used as a negation.