Q From Carol Llewellyn: What is the origin of the word doughboy as in a U.S. Infantryman, especially one of World War I. Do you know why they were called this?
A The word has at various times been used to refer to a dumpling (in the British Navy mainly), for a kind of doughnut, and as a corruption of the Spanish word adobe.
The sense you refer to was first recorded in reference to the American Civil War. One theory is that the big round brass buttons on infantry uniforms reminded people of doughnuts, and the word was soon transferred from the buttons to the soldiers wearing the uniform.
Another theory is that it derives from the use of pipe clay “dough” to clean the infantrymen’s white belts. It has also been suggested that it comes from adobe, which it seems was once used as a slang term in the American south-west for soldiers, but this sounds less likely.