As a noun, desert differs in spelling, pronunciation, and meaning from dessert. The term for an arid region is pronounced "DEZ-uhrt." The term for a pastry, pudding, or other final course of a meal is pronounced "di-ZUHRT," as is the verb desert: "While roaming in the desert he had to do without dessert." "Do not desert your job now." The word desert, as in "just deserts," has nothing to do with either arid regions or sweet concoctions. It derives from the same root as deserves and means "rewards or punishments": "Every contestant will receive his just deserts."
Dictionary of problem words and expressions. Harry Shaw. 1975.