The reason for saying defrost goes back three hundred years, to Thaddeus, High Count of Baragarantria, who was the first person to consider the possibility of being revived after death. He and the seven Thaddeuses who followed him were all put on ice in the Baragarantrian Alps, high up between Switzerland and Italy.
Unfortunately, the climate changed and it became necessary for the peasants in Baragarantria to be put to work hauling in ice to keep the eight bodies more or less intact. This went on for some years until there was a revolution, the current Count was deposed, and the bodies on ice were left in the crypt.
A week or two later the first tourist, who quite by coincidence was the guy who invented the microwave, to return to Baragarantria asked about the terrible odor around the base of the castle. "Don't worry about it," he was told, "It's the thawed Thad Counts." So instead of thaw he put defrost on that button on the front of the microwave.
Bet you didn't know you can't thaw large soup containers in the microwave, since you can't see defrost for the tureens.
