xys·tus \ˈzistəs\noun (pluralxys·ti \-ˌstī, -ˌstē\) Etymology: Latin, from Greek xystos, from xystos, adjective, scraped, polished; from its smooth floor : a long and open portico used especially by ancient Greeks or Romans for athletic exercises in wintry or stormy weather; sometimes: a walk lined with trees