In this week's New Yorker, Annie Proulx uses the unusual xanthine in her short story "Rough Deeds":
One October afternoon, they landed their canoe on a sandy Maine river shore fronting one of their new white-pine properties, twenty thousand acres at a cost of twelve cents an acre. There was a narrow hem of ice along the shaded shoreline.
"Frog ice," Forgeron said. In the rich autumn light, the deciduous trees stunned with xanthine orange and yellow. The men's swart shadows fell on the ground like toppled statues.
Xanthine derives from the Greek xanthos for yellow, and in this context, it's meant to suggest a yellow tint to orange leaves. However, in this particular story, which spares no reference to infection, murder, brutal accidents, torture, disease, and bodily decay among timber "voyaguers" and thieves in colonial New England, Proulx is likely invoking xanthine's noun form — it's the name of a chemical compound related to blood and urine — to suggest that to the humans in "Rought Deeds," even the living trees seem stained with human waste.
Other four-star choices in "Rough Deeds" include: miasma, swart, smote, cipher, vermin, hoarfrost, boardfeet, gibbous, eponymous, conflagration, deleterious, bugbear, quinsy, maelstrom, insensate, and putrid. Check them out in list form here.