from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Between the ages of 20 and 29, inclusive. In one's third decade.
- n. A person whose age is between twenty and twenty-nine years, inclusive; someone in his or her twenties. Someone in his or her third decade.
From Latin vicenārius ("of or containing twenty"), from vigintī ("twenty") + -an (Wiktionary)