Arrantly is an archaic term that means "proudly or arrogantly." There are several synonyms for this word that can be used in modern English. One such word is brazenly, which means "boldly and shamelessly." Another synonym is audaciously, which implies boldness and daring. A related term is flagrantly, which refers to something that is done in an obviously wrong or immoral way. Other synonyms that could be used include boldly, openly, and shamelessly. While arrantly may be an uncommon word that is no longer in regular use, there are several alternative terms that convey a similar meaning.