xyst (z?st) , xystus or xystosn1. (Architecture) a long portico, esp one used in ancient Greece for athletics2. (Architecture) (in ancient Rome) a covered garden walk or one lined with trees[C17: from Latin xystus, from Greek xustos, literally: smoothed, polished (area), from xuein to scrape, make smooth]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014