Xander, var. Xan, Xandro, means "man's defender". Xan and Xandro are more rarefied as forms of Xander.
Xanthus, var. Xanthos, means "golden-haired". Xanthus and Xanthos are unusual first names, and Xanthos is found frequently (upper 61%) as a last name.
Xavier, var. Xavi, Xever, Xayvion, Xaviell, Xathieur, means "new house". Xavier, Xavi, etc. became less trendy in 2014, dropping -76 rankings as boys' names with Xavi leading the fall.
Xenophon, var. Xeno, means "foreign voice". Outside Top 1000.
Xenos, means "hospitality". Not Top 1000 name.
Xerxes, means "monarch". Not Top 1000 name.
Xidorn, means "truth-seeker". Not Top 1000 name.
Ximenes, var. Ximenez, means "to listen". Ximenes and Ximenez are scarcely used as first names, and Ximenez appears frequently (top 40%) as a last name.
Xiomar, means "famous in battle". Uncommon. Compare Xiomar and common -mar surnames Romar (upper 48%), Qamar (37%).