Mettlesomely is defined as being full of courage, vigor, and resilience. There are several synonyms that can be used to describe someone showing these traits. Brave, fearless, bold, audacious, and gallant are just a few of the words that can be used in place of mettlesomely. Other terms that could be used include intrepid, valiant, plucky, and spunky. These words all convey a sense of strength, determination, and courage, which are the hallmarks of someone who is mettlesome. Whether describing a person or their actions, these words are all excellent choices for capturing the spirit of someone who is mettlesome.