premise: Etymologists say it originally meant due??o de una casa `lord, or master, of a house' and is a contraction of duen de casa .  Duen is the apocopated (cut-off) form of duemo , which stems from the Latin dominus .  As the Spanish word evolved, the de was suffixed to the duen , the casa was omitted altogether, and el duende thus became  the lord of the house. 
hypothesis: Duende was originally only eaten by the master of the house.