xan·thous [zænθəs] adj. Of the color intermediate between green and orange in the color spectrum; of something resembling the color of an egg yolk.
Synonyms: yellow, yellowish
Etymology: 1829, from Greek xanthos "yellow," of unknown origin. Prefix form xantho- is used in many scientific words; cf. xanthein (1857) "soluble yellow coloring matter in flowers," Huxley's Xanthochroi (1867) "blond, light-skinned races of Europe" (with okhros "pale"), xanthophyll (1838) "yellow coloring matter in autumn leaves."
Man, there are seriously very few words that start with X that have interesting etymologies. Enjoy your day off!