The Search for Delicious — Natalie Babbitt

Gaylen, the King's messenger, a skinny boy of twelve, is off to poll the kingdom, traveling from town to farmstead to town on his horse, Marrow. At first it is merely a question of disagreement at the royal castle over which food should stand for Delicious in the new dictionary. But soon it seems that the search for Delicious had better succeed if civil war is to be avoided.

Gaylen's quest leads him to the woldweller, a wise, 900-year-old creature who lives alone at the precise center of the forest; to Canto, the minstrel who sings him an old song about a mermaid child and who gives him a peculiar good-luck charm; to the underground domain of the dwarfs; and finally to Ardis who might save the kingdom from havoc.