The Collaborative International Dictionary
Xantho-
Xantho- \Xan"tho-\ A combining form from Gr. xanqo`s yellow; as in xanthocobaltic salts. Used also adjectively in chemistry.
Douglas Harper's Etymology Dictionary
xantho-
before vowels xanth-, word-forming element meaning "yellow," from Greek xanthos "yellow" of various shades; used especially of hair and horses, of unknown origin. Used in scientific words; such as xanthein (1857) "soluble yellow coloring matter in flowers," xanthophyll (1838) "yellow coloring matter in autumn leaves." Also Huxley's Xanthochroi (1867) "blond, light-skinned races of Europe" (with okhros "pale").
Wiktionary
xantho-
pre. 1 yellow 2 (context chemistry English) derivative of xanthic acid