The word "rankles" means to cause persistent irritation or resentment. There are several synonyms to this word such as "gnaws", "chafes", "grates", "nettles", "irritates" and "vexes". All these words denote a feeling of irritation, annoyance or displeasure that is constantly present. Similarly, all these words create a sense of persistent agitation or annoyance that can prove to be quite uncomfortable. The choice of synonyms depends on the context in which they are being used. Overall, all the synonyms for "rankles" carry the same connotation of negative feeling persisting over a duration of time.